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  70. <a name="Machine-Modes"></a>

  71. <div class="header">

  72. <p>

  73. Next: <a href="Constants.html#Constants" accesskey="n" rel="next">Constants</a>, Previous: <a href="Flags.html#Flags" accesskey="p" rel="prev">Flags</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>

  74. </div>

  75. <hr>

  76. <a name="Machine-Modes-1"></a>

  77. <h3 class="section">14.6 Machine Modes</h3>

  78. <a name="index-machine-modes"></a>

  79. 

  80. <a name="index-machine_005fmode"></a>

  81. <p>A machine mode describes a size of data object and the representation used

  82. for it.  In the C code, machine modes are represented by an enumeration

  83. type, <code>machine_mode</code>, defined in <samp>machmode.def</samp>.  Each RTL

  84. expression has room for a machine mode and so do certain kinds of tree

  85. expressions (declarations and types, to be precise).

  86. </p>

  87. <p>In debugging dumps and machine descriptions, the machine mode of an RTL

  88. expression is written after the expression code with a colon to separate

  89. them.  The letters &lsquo;<samp>mode</samp>&rsquo; which appear at the end of each machine mode

  90. name are omitted.  For example, <code>(reg:SI 38)</code> is a <code>reg</code>

  91. expression with machine mode <code>SImode</code>.  If the mode is

  92. <code>VOIDmode</code>, it is not written at all.

  93. </p>

  94. <p>Here is a table of machine modes.  The term &ldquo;byte&rdquo; below refers to an

  95. object of <code>BITS_PER_UNIT</code> bits (see <a href="Storage-Layout.html#Storage-Layout">Storage Layout</a>).

  96. </p>

  97. <dl compact="compact">

  98. <dd><a name="index-BImode"></a>

  99. </dd>

  100. <dt><code>BImode</code></dt>

  101. <dd><p>&ldquo;Bit&rdquo; mode represents a single bit, for predicate registers.

  102. </p>

  103. <a name="index-QImode"></a>

  104. </dd>

  105. <dt><code>QImode</code></dt>

  106. <dd><p>&ldquo;Quarter-Integer&rdquo; mode represents a single byte treated as an integer.

  107. </p>

  108. <a name="index-HImode"></a>

  109. </dd>

  110. <dt><code>HImode</code></dt>

  111. <dd><p>&ldquo;Half-Integer&rdquo; mode represents a two-byte integer.

  112. </p>

  113. <a name="index-PSImode"></a>

  114. </dd>

  115. <dt><code>PSImode</code></dt>

  116. <dd><p>&ldquo;Partial Single Integer&rdquo; mode represents an integer which occupies

  117. four bytes but which doesn&rsquo;t really use all four.  On some machines,

  118. this is the right mode to use for pointers.

  119. </p>

  120. <a name="index-SImode"></a>

  121. </dd>

  122. <dt><code>SImode</code></dt>

  123. <dd><p>&ldquo;Single Integer&rdquo; mode represents a four-byte integer.

  124. </p>

  125. <a name="index-PDImode"></a>

  126. </dd>

  127. <dt><code>PDImode</code></dt>

  128. <dd><p>&ldquo;Partial Double Integer&rdquo; mode represents an integer which occupies

  129. eight bytes but which doesn&rsquo;t really use all eight.  On some machines,

  130. this is the right mode to use for certain pointers.

  131. </p>

  132. <a name="index-DImode"></a>

  133. </dd>

  134. <dt><code>DImode</code></dt>

  135. <dd><p>&ldquo;Double Integer&rdquo; mode represents an eight-byte integer.

  136. </p>

  137. <a name="index-TImode"></a>

  138. </dd>

  139. <dt><code>TImode</code></dt>

  140. <dd><p>&ldquo;Tetra Integer&rdquo; (?) mode represents a sixteen-byte integer.

  141. </p>

  142. <a name="index-OImode"></a>

  143. </dd>

  144. <dt><code>OImode</code></dt>

  145. <dd><p>&ldquo;Octa Integer&rdquo; (?) mode represents a thirty-two-byte integer.

  146. </p>

  147. <a name="index-XImode"></a>

  148. </dd>

  149. <dt><code>XImode</code></dt>

  150. <dd><p>&ldquo;Hexadeca Integer&rdquo; (?) mode represents a sixty-four-byte integer.

  151. </p>

  152. <a name="index-QFmode"></a>

  153. </dd>

  154. <dt><code>QFmode</code></dt>

  155. <dd><p>&ldquo;Quarter-Floating&rdquo; mode represents a quarter-precision (single byte)

  156. floating point number.

  157. </p>

  158. <a name="index-HFmode"></a>

  159. </dd>

  160. <dt><code>HFmode</code></dt>

  161. <dd><p>&ldquo;Half-Floating&rdquo; mode represents a half-precision (two byte) floating

  162. point number.

  163. </p>

  164. <a name="index-TQFmode"></a>

  165. </dd>

  166. <dt><code>TQFmode</code></dt>

  167. <dd><p>&ldquo;Three-Quarter-Floating&rdquo; (?) mode represents a three-quarter-precision

  168. (three byte) floating point number.

  169. </p>

  170. <a name="index-SFmode"></a>

  171. </dd>

  172. <dt><code>SFmode</code></dt>

  173. <dd><p>&ldquo;Single Floating&rdquo; mode represents a four byte floating point number.

  174. In the common case, of a processor with IEEE arithmetic and 8-bit bytes,

  175. this is a single-precision IEEE floating point number; it can also be

  176. used for double-precision (on processors with 16-bit bytes) and

  177. single-precision VAX and IBM types.

  178. </p>

  179. <a name="index-DFmode"></a>

  180. </dd>

  181. <dt><code>DFmode</code></dt>

  182. <dd><p>&ldquo;Double Floating&rdquo; mode represents an eight byte floating point number.

  183. In the common case, of a processor with IEEE arithmetic and 8-bit bytes,

  184. this is a double-precision IEEE floating point number.

  185. </p>

  186. <a name="index-XFmode"></a>

  187. </dd>

  188. <dt><code>XFmode</code></dt>

  189. <dd><p>&ldquo;Extended Floating&rdquo; mode represents an IEEE extended floating point

  190. number.  This mode only has 80 meaningful bits (ten bytes).  Some

  191. processors require such numbers to be padded to twelve bytes, others

  192. to sixteen; this mode is used for either.

  193. </p>

  194. <a name="index-SDmode"></a>

  195. </dd>

  196. <dt><code>SDmode</code></dt>

  197. <dd><p>&ldquo;Single Decimal Floating&rdquo; mode represents a four byte decimal

  198. floating point number (as distinct from conventional binary floating

  199. point).

  200. </p>

  201. <a name="index-DDmode"></a>

  202. </dd>

  203. <dt><code>DDmode</code></dt>

  204. <dd><p>&ldquo;Double Decimal Floating&rdquo; mode represents an eight byte decimal

  205. floating point number.

  206. </p>

  207. <a name="index-TDmode"></a>

  208. </dd>

  209. <dt><code>TDmode</code></dt>

  210. <dd><p>&ldquo;Tetra Decimal Floating&rdquo; mode represents a sixteen byte decimal

  211. floating point number all 128 of whose bits are meaningful.

  212. </p>

  213. <a name="index-TFmode"></a>

  214. </dd>

  215. <dt><code>TFmode</code></dt>

  216. <dd><p>&ldquo;Tetra Floating&rdquo; mode represents a sixteen byte floating point number

  217. all 128 of whose bits are meaningful.  One common use is the

  218. IEEE quad-precision format.

  219. </p>

  220. <a name="index-QQmode"></a>

  221. </dd>

  222. <dt><code>QQmode</code></dt>

  223. <dd><p>&ldquo;Quarter-Fractional&rdquo; mode represents a single byte treated as a signed

  224. fractional number.  The default format is &ldquo;s.7&rdquo;.

  225. </p>

  226. <a name="index-HQmode"></a>

  227. </dd>

  228. <dt><code>HQmode</code></dt>

  229. <dd><p>&ldquo;Half-Fractional&rdquo; mode represents a two-byte signed fractional number.

  230. The default format is &ldquo;s.15&rdquo;.

  231. </p>

  232. <a name="index-SQmode"></a>

  233. </dd>

  234. <dt><code>SQmode</code></dt>

  235. <dd><p>&ldquo;Single Fractional&rdquo; mode represents a four-byte signed fractional number.

  236. The default format is &ldquo;s.31&rdquo;.

  237. </p>

  238. <a name="index-DQmode"></a>

  239. </dd>

  240. <dt><code>DQmode</code></dt>

  241. <dd><p>&ldquo;Double Fractional&rdquo; mode represents an eight-byte signed fractional number.

  242. The default format is &ldquo;s.63&rdquo;.

  243. </p>

  244. <a name="index-TQmode"></a>

  245. </dd>

  246. <dt><code>TQmode</code></dt>

  247. <dd><p>&ldquo;Tetra Fractional&rdquo; mode represents a sixteen-byte signed fractional number.

  248. The default format is &ldquo;s.127&rdquo;.

  249. </p>

  250. <a name="index-UQQmode"></a>

  251. </dd>

  252. <dt><code>UQQmode</code></dt>

  253. <dd><p>&ldquo;Unsigned Quarter-Fractional&rdquo; mode represents a single byte treated as an

  254. unsigned fractional number.  The default format is &ldquo;.8&rdquo;.

  255. </p>

  256. <a name="index-UHQmode"></a>

  257. </dd>

  258. <dt><code>UHQmode</code></dt>

  259. <dd><p>&ldquo;Unsigned Half-Fractional&rdquo; mode represents a two-byte unsigned fractional

  260. number.  The default format is &ldquo;.16&rdquo;.

  261. </p>

  262. <a name="index-USQmode"></a>

  263. </dd>

  264. <dt><code>USQmode</code></dt>

  265. <dd><p>&ldquo;Unsigned Single Fractional&rdquo; mode represents a four-byte unsigned fractional

  266. number.  The default format is &ldquo;.32&rdquo;.

  267. </p>

  268. <a name="index-UDQmode"></a>

  269. </dd>

  270. <dt><code>UDQmode</code></dt>

  271. <dd><p>&ldquo;Unsigned Double Fractional&rdquo; mode represents an eight-byte unsigned

  272. fractional number.  The default format is &ldquo;.64&rdquo;.

  273. </p>

  274. <a name="index-UTQmode"></a>

  275. </dd>

  276. <dt><code>UTQmode</code></dt>

  277. <dd><p>&ldquo;Unsigned Tetra Fractional&rdquo; mode represents a sixteen-byte unsigned

  278. fractional number.  The default format is &ldquo;.128&rdquo;.

  279. </p>

  280. <a name="index-HAmode"></a>

  281. </dd>

  282. <dt><code>HAmode</code></dt>

  283. <dd><p>&ldquo;Half-Accumulator&rdquo; mode represents a two-byte signed accumulator.

  284. The default format is &ldquo;s8.7&rdquo;.

  285. </p>

  286. <a name="index-SAmode"></a>

  287. </dd>

  288. <dt><code>SAmode</code></dt>

  289. <dd><p>&ldquo;Single Accumulator&rdquo; mode represents a four-byte signed accumulator.

  290. The default format is &ldquo;s16.15&rdquo;.

  291. </p>

  292. <a name="index-DAmode"></a>

  293. </dd>

  294. <dt><code>DAmode</code></dt>

  295. <dd><p>&ldquo;Double Accumulator&rdquo; mode represents an eight-byte signed accumulator.

  296. The default format is &ldquo;s32.31&rdquo;.

  297. </p>

  298. <a name="index-TAmode"></a>

  299. </dd>

  300. <dt><code>TAmode</code></dt>

  301. <dd><p>&ldquo;Tetra Accumulator&rdquo; mode represents a sixteen-byte signed accumulator.

  302. The default format is &ldquo;s64.63&rdquo;.

  303. </p>

  304. <a name="index-UHAmode"></a>

  305. </dd>

  306. <dt><code>UHAmode</code></dt>

  307. <dd><p>&ldquo;Unsigned Half-Accumulator&rdquo; mode represents a two-byte unsigned accumulator.

  308. The default format is &ldquo;8.8&rdquo;.

  309. </p>

  310. <a name="index-USAmode"></a>

  311. </dd>

  312. <dt><code>USAmode</code></dt>

  313. <dd><p>&ldquo;Unsigned Single Accumulator&rdquo; mode represents a four-byte unsigned

  314. accumulator.  The default format is &ldquo;16.16&rdquo;.

  315. </p>

  316. <a name="index-UDAmode"></a>

  317. </dd>

  318. <dt><code>UDAmode</code></dt>

  319. <dd><p>&ldquo;Unsigned Double Accumulator&rdquo; mode represents an eight-byte unsigned

  320. accumulator.  The default format is &ldquo;32.32&rdquo;.

  321. </p>

  322. <a name="index-UTAmode"></a>

  323. </dd>

  324. <dt><code>UTAmode</code></dt>

  325. <dd><p>&ldquo;Unsigned Tetra Accumulator&rdquo; mode represents a sixteen-byte unsigned

  326. accumulator.  The default format is &ldquo;64.64&rdquo;.

  327. </p>

  328. <a name="index-CCmode"></a>

  329. </dd>

  330. <dt><code>CCmode</code></dt>

  331. <dd><p>&ldquo;Condition Code&rdquo; mode represents the value of a condition code, which

  332. is a machine-specific set of bits used to represent the result of a

  333. comparison operation.  Other machine-specific modes may also be used for

  334. the condition code.  These modes are not used on machines that use

  335. <code>cc0</code> (see <a href="Condition-Code.html#Condition-Code">Condition Code</a>).

  336. </p>

  337. <a name="index-BLKmode"></a>

  338. </dd>

  339. <dt><code>BLKmode</code></dt>

  340. <dd><p>&ldquo;Block&rdquo; mode represents values that are aggregates to which none of

  341. the other modes apply.  In RTL, only memory references can have this mode,

  342. and only if they appear in string-move or vector instructions.  On machines

  343. which have no such instructions, <code>BLKmode</code> will not appear in RTL.

  344. </p>

  345. <a name="index-VOIDmode"></a>

  346. </dd>

  347. <dt><code>VOIDmode</code></dt>

  348. <dd><p>Void mode means the absence of a mode or an unspecified mode.

  349. For example, RTL expressions of code <code>const_int</code> have mode

  350. <code>VOIDmode</code> because they can be taken to have whatever mode the context

  351. requires.  In debugging dumps of RTL, <code>VOIDmode</code> is expressed by

  352. the absence of any mode.

  353. </p>

  354. <a name="index-QCmode"></a>

  355. <a name="index-HCmode"></a>

  356. <a name="index-SCmode"></a>

  357. <a name="index-DCmode"></a>

  358. <a name="index-XCmode"></a>

  359. <a name="index-TCmode"></a>

  360. </dd>

  361. <dt><code>QCmode, HCmode, SCmode, DCmode, XCmode, TCmode</code></dt>

  362. <dd><p>These modes stand for a complex number represented as a pair of floating

  363. point values.  The floating point values are in <code>QFmode</code>,

  364. <code>HFmode</code>, <code>SFmode</code>, <code>DFmode</code>, <code>XFmode</code>, and

  365. <code>TFmode</code>, respectively.

  366. </p>

  367. <a name="index-CQImode"></a>

  368. <a name="index-CHImode"></a>

  369. <a name="index-CSImode"></a>

  370. <a name="index-CDImode"></a>

  371. <a name="index-CTImode"></a>

  372. <a name="index-COImode"></a>

  373. <a name="index-CPSImode"></a>

  374. </dd>

  375. <dt><code>CQImode, CHImode, CSImode, CDImode, CTImode, COImode, CPSImode</code></dt>

  376. <dd><p>These modes stand for a complex number represented as a pair of integer

  377. values.  The integer values are in <code>QImode</code>, <code>HImode</code>,

  378. <code>SImode</code>, <code>DImode</code>, <code>TImode</code>, <code>OImode</code>, and <code>PSImode</code>,

  379. respectively.

  380. </p>

  381. <a name="index-BND32mode"></a>

  382. <a name="index-BND64mode"></a>

  383. </dd>

  384. <dt><code>BND32mode BND64mode</code></dt>

  385. <dd><p>These modes stand for bounds for pointer of 32 and 64 bit size respectively.

  386. Mode size is double pointer mode size.

  387. </p></dd>

  388. </dl>

  389. 

  390. <p>The machine description defines <code>Pmode</code> as a C macro which expands

  391. into the machine mode used for addresses.  Normally this is the mode

  392. whose size is <code>BITS_PER_WORD</code>, <code>SImode</code> on 32-bit machines.

  393. </p>

  394. <p>The only modes which a machine description <i>must</i> support are

  395. <code>QImode</code>, and the modes corresponding to <code>BITS_PER_WORD</code>,

  396. <code>FLOAT_TYPE_SIZE</code> and <code>DOUBLE_TYPE_SIZE</code>.

  397. The compiler will attempt to use <code>DImode</code> for 8-byte structures and

  398. unions, but this can be prevented by overriding the definition of

  399. <code>MAX_FIXED_MODE_SIZE</code>.  Alternatively, you can have the compiler

  400. use <code>TImode</code> for 16-byte structures and unions.  Likewise, you can

  401. arrange for the C type <code>short int</code> to avoid using <code>HImode</code>.

  402. </p>

  403. <a name="index-mode-classes"></a>

  404. <p>Very few explicit references to machine modes remain in the compiler and

  405. these few references will soon be removed.  Instead, the machine modes

  406. are divided into mode classes.  These are represented by the enumeration

  407. type <code>enum mode_class</code> defined in <samp>machmode.h</samp>.  The possible

  408. mode classes are:

  409. </p>

  410. <dl compact="compact">

  411. <dd><a name="index-MODE_005fINT"></a>

  412. </dd>

  413. <dt><code>MODE_INT</code></dt>

  414. <dd><p>Integer modes.  By default these are <code>BImode</code>, <code>QImode</code>,

  415. <code>HImode</code>, <code>SImode</code>, <code>DImode</code>, <code>TImode</code>, and

  416. <code>OImode</code>.

  417. </p>

  418. <a name="index-MODE_005fPARTIAL_005fINT"></a>

  419. </dd>

  420. <dt><code>MODE_PARTIAL_INT</code></dt>

  421. <dd><p>The &ldquo;partial integer&rdquo; modes, <code>PQImode</code>, <code>PHImode</code>,

  422. <code>PSImode</code> and <code>PDImode</code>.

  423. </p>

  424. <a name="index-MODE_005fFLOAT"></a>

  425. </dd>

  426. <dt><code>MODE_FLOAT</code></dt>

  427. <dd><p>Floating point modes.  By default these are <code>QFmode</code>,

  428. <code>HFmode</code>, <code>TQFmode</code>, <code>SFmode</code>, <code>DFmode</code>,

  429. <code>XFmode</code> and <code>TFmode</code>.

  430. </p>

  431. <a name="index-MODE_005fDECIMAL_005fFLOAT"></a>

  432. </dd>

  433. <dt><code>MODE_DECIMAL_FLOAT</code></dt>

  434. <dd><p>Decimal floating point modes.  By default these are <code>SDmode</code>,

  435. <code>DDmode</code> and <code>TDmode</code>.

  436. </p>

  437. <a name="index-MODE_005fFRACT"></a>

  438. </dd>

  439. <dt><code>MODE_FRACT</code></dt>

  440. <dd><p>Signed fractional modes.  By default these are <code>QQmode</code>, <code>HQmode</code>,

  441. <code>SQmode</code>, <code>DQmode</code> and <code>TQmode</code>.

  442. </p>

  443. <a name="index-MODE_005fUFRACT"></a>

  444. </dd>

  445. <dt><code>MODE_UFRACT</code></dt>

  446. <dd><p>Unsigned fractional modes.  By default these are <code>UQQmode</code>, <code>UHQmode</code>,

  447. <code>USQmode</code>, <code>UDQmode</code> and <code>UTQmode</code>.

  448. </p>

  449. <a name="index-MODE_005fACCUM"></a>

  450. </dd>

  451. <dt><code>MODE_ACCUM</code></dt>

  452. <dd><p>Signed accumulator modes.  By default these are <code>HAmode</code>,

  453. <code>SAmode</code>, <code>DAmode</code> and <code>TAmode</code>.

  454. </p>

  455. <a name="index-MODE_005fUACCUM"></a>

  456. </dd>

  457. <dt><code>MODE_UACCUM</code></dt>

  458. <dd><p>Unsigned accumulator modes.  By default these are <code>UHAmode</code>,

  459. <code>USAmode</code>, <code>UDAmode</code> and <code>UTAmode</code>.

  460. </p>

  461. <a name="index-MODE_005fCOMPLEX_005fINT"></a>

  462. </dd>

  463. <dt><code>MODE_COMPLEX_INT</code></dt>

  464. <dd><p>Complex integer modes.  (These are not currently implemented).

  465. </p>

  466. <a name="index-MODE_005fCOMPLEX_005fFLOAT"></a>

  467. </dd>

  468. <dt><code>MODE_COMPLEX_FLOAT</code></dt>

  469. <dd><p>Complex floating point modes.  By default these are <code>QCmode</code>,

  470. <code>HCmode</code>, <code>SCmode</code>, <code>DCmode</code>, <code>XCmode</code>, and

  471. <code>TCmode</code>.

  472. </p>

  473. <a name="index-MODE_005fCC"></a>

  474. </dd>

  475. <dt><code>MODE_CC</code></dt>

  476. <dd><p>Modes representing condition code values.  These are <code>CCmode</code> plus

  477. any <code>CC_MODE</code> modes listed in the <samp><var>machine</var>-modes.def</samp>.

  478. See <a href="Jump-Patterns.html#Jump-Patterns">Jump Patterns</a>,

  479. also see <a href="Condition-Code.html#Condition-Code">Condition Code</a>.

  480. </p>

  481. <a name="index-MODE_005fPOINTER_005fBOUNDS"></a>

  482. </dd>

  483. <dt><code>MODE_POINTER_BOUNDS</code></dt>

  484. <dd><p>Pointer bounds modes.  Used to represent values of pointer bounds type.

  485. Operations in these modes may be executed as NOPs depending on hardware

  486. features and environment setup.

  487. </p>

  488. <a name="index-MODE_005fRANDOM"></a>

  489. </dd>

  490. <dt><code>MODE_RANDOM</code></dt>

  491. <dd><p>This is a catchall mode class for modes which don&rsquo;t fit into the above

  492. classes.  Currently <code>VOIDmode</code> and <code>BLKmode</code> are in

  493. <code>MODE_RANDOM</code>.

  494. </p></dd>

  495. </dl>

  496. 

  497. <a name="index-machine-mode-wrapper-classes"></a>

  498. <p><code>machmode.h</code> also defines various wrapper classes that combine a

  499. <code>machine_mode</code> with a static assertion that a particular

  500. condition holds.  The classes are:

  501. </p>

  502. <dl compact="compact">

  503. <dd><a name="index-scalar_005fint_005fmode"></a>

  504. </dd>

  505. <dt><code>scalar_int_mode</code></dt>

  506. <dd><p>A mode that has class <code>MODE_INT</code> or <code>MODE_PARTIAL_INT</code>.

  507. </p>

  508. <a name="index-scalar_005ffloat_005fmode"></a>

  509. </dd>

  510. <dt><code>scalar_float_mode</code></dt>

  511. <dd><p>A mode that has class <code>MODE_FLOAT</code> or <code>MODE_DECIMAL_FLOAT</code>.

  512. </p>

  513. <a name="index-scalar_005fmode"></a>

  514. </dd>

  515. <dt><code>scalar_mode</code></dt>

  516. <dd><p>A mode that holds a single numerical value.  In practice this means

  517. that the mode is a <code>scalar_int_mode</code>, is a <code>scalar_float_mode</code>,

  518. or has class <code>MODE_FRACT</code>, <code>MODE_UFRACT</code>, <code>MODE_ACCUM</code>,

  519. <code>MODE_UACCUM</code> or <code>MODE_POINTER_BOUNDS</code>.

  520. </p>

  521. <a name="index-complex_005fmode"></a>

  522. </dd>

  523. <dt><code>complex_mode</code></dt>

  524. <dd><p>A mode that has class <code>MODE_COMPLEX_INT</code> or <code>MODE_COMPLEX_FLOAT</code>.

  525. </p>

  526. <a name="index-fixed_005fsize_005fmode"></a>

  527. </dd>

  528. <dt><code>fixed_size_mode</code></dt>

  529. <dd><p>A mode whose size is known at compile time.

  530. </p></dd>

  531. </dl>

  532. 

  533. <p>Named modes use the most constrained of the available wrapper classes,

  534. if one exists, otherwise they use <code>machine_mode</code>.  For example,

  535. <code>QImode</code> is a <code>scalar_int_mode</code>, <code>SFmode</code> is a

  536. <code>scalar_float_mode</code> and <code>BLKmode</code> is a plain

  537. <code>machine_mode</code>.  It is possible to refer to any mode as a raw

  538. <code>machine_mode</code> by adding the <code>E_</code> prefix, where <code>E</code>

  539. stands for &ldquo;enumeration&rdquo;.  For example, the raw <code>machine_mode</code>

  540. names of the modes just mentioned are <code>E_QImode</code>, <code>E_SFmode</code>

  541. and <code>E_BLKmode</code> respectively.

  542. </p>

  543. <p>The wrapper classes implicitly convert to <code>machine_mode</code> and to any

  544. wrapper class that represents a more general condition; for example

  545. <code>scalar_int_mode</code> and <code>scalar_float_mode</code> both convert

  546. to <code>scalar_mode</code> and all three convert to <code>fixed_size_mode</code>.

  547. The classes act like <code>machine_mode</code>s that accept only certain

  548. named modes.

  549. </p>

  550. <a name="index-opt_005fmode"></a>

  551. <p><samp>machmode.h</samp> also defines a template class <code>opt_mode&lt;<var>T</var>&gt;</code>

  552. that holds a <code>T</code> or nothing, where <code>T</code> can be either

  553. <code>machine_mode</code> or one of the wrapper classes above.  The main

  554. operations on an <code>opt_mode&lt;<var>T</var>&gt;</code> <var>x</var> are as follows:

  555. </p>

  556. <dl compact="compact">

  557. <dt>&lsquo;<samp><var>x</var>.exists ()</samp>&rsquo;</dt>

  558. <dd><p>Return true if <var>x</var> holds a mode rather than nothing.

  559. </p>

  560. </dd>

  561. <dt>&lsquo;<samp><var>x</var>.exists (&amp;<var>y</var>)</samp>&rsquo;</dt>

  562. <dd><p>Return true if <var>x</var> holds a mode rather than nothing, storing the

  563. mode in <var>y</var> if so.  <var>y</var> must be assignment-compatible with <var>T</var>.

  564. </p>

  565. </dd>

  566. <dt>&lsquo;<samp><var>x</var>.require ()</samp>&rsquo;</dt>

  567. <dd><p>Assert that <var>x</var> holds a mode rather than nothing and return that mode.

  568. </p>

  569. </dd>

  570. <dt>&lsquo;<samp><var>x</var> = <var>y</var></samp>&rsquo;</dt>

  571. <dd><p>Set <var>x</var> to <var>y</var>, where <var>y</var> is a <var>T</var> or implicitly converts

  572. to a <var>T</var>.

  573. </p></dd>

  574. </dl>

  575. 

  576. <p>The default constructor sets an <code>opt_mode&lt;<var>T</var>&gt;</code> to nothing.

  577. There is also a constructor that takes an initial value of type <var>T</var>.

  578. </p>

  579. <p>It is possible to use the <samp>is-a.h</samp> accessors on a <code>machine_mode</code>

  580. or machine mode wrapper <var>x</var>:

  581. </p>

  582. <dl compact="compact">

  583. <dd><a name="index-is_005fa"></a>

  584. </dd>

  585. <dt>&lsquo;<samp>is_a &lt;<var>T</var>&gt; (<var>x</var>)</samp>&rsquo;</dt>

  586. <dd><p>Return true if <var>x</var> meets the conditions for wrapper class <var>T</var>.

  587. </p>

  588. </dd>

  589. <dt>&lsquo;<samp>is_a &lt;<var>T</var>&gt; (<var>x</var>, &amp;<var>y</var>)</samp>&rsquo;</dt>

  590. <dd><p>Return true if <var>x</var> meets the conditions for wrapper class <var>T</var>,

  591. storing it in <var>y</var> if so.  <var>y</var> must be assignment-compatible with

  592. <var>T</var>.

  593. </p>

  594. </dd>

  595. <dt>&lsquo;<samp>as_a &lt;<var>T</var>&gt; (<var>x</var>)</samp>&rsquo;</dt>

  596. <dd><p>Assert that <var>x</var> meets the conditions for wrapper class <var>T</var>

  597. and return it as a <var>T</var>.

  598. </p>

  599. </dd>

  600. <dt>&lsquo;<samp>dyn_cast &lt;<var>T</var>&gt; (<var>x</var>)</samp>&rsquo;</dt>

  601. <dd><p>Return an <code>opt_mode&lt;<var>T</var>&gt;</code> that holds <var>x</var> if <var>x</var> meets

  602. the conditions for wrapper class <var>T</var> and that holds nothing otherwise.

  603. </p></dd>

  604. </dl>

  605. 

  606. <p>The purpose of these wrapper classes is to give stronger static type

  607. checking.  For example, if a function takes a <code>scalar_int_mode</code>,

  608. a caller that has a general <code>machine_mode</code> must either check or

  609. assert that the code is indeed a scalar integer first, using one of

  610. the functions above.

  611. </p>

  612. <p>The wrapper classes are normal C++ classes, with user-defined

  613. constructors.  Sometimes it is useful to have a POD version of

  614. the same type, particularly if the type appears in a <code>union</code>.

  615. The template class <code>pod_mode&lt;<var>T</var>&gt;</code> provides a POD version

  616. of wrapper class <var>T</var>.  It is assignment-compatible with <var>T</var>

  617. and implicitly converts to both <code>machine_mode</code> and <var>T</var>.

  618. </p>

  619. <p>Here are some C macros that relate to machine modes:

  620. </p>

  621. <dl compact="compact">

  622. <dd><a name="index-GET_005fMODE"></a>

  623. </dd>

  624. <dt><code>GET_MODE (<var>x</var>)</code></dt>

  625. <dd><p>Returns the machine mode of the RTX <var>x</var>.

  626. </p>

  627. <a name="index-PUT_005fMODE"></a>

  628. </dd>

  629. <dt><code>PUT_MODE (<var>x</var>, <var>newmode</var>)</code></dt>

  630. <dd><p>Alters the machine mode of the RTX <var>x</var> to be <var>newmode</var>.

  631. </p>

  632. <a name="index-NUM_005fMACHINE_005fMODES"></a>

  633. </dd>

  634. <dt><code>NUM_MACHINE_MODES</code></dt>

  635. <dd><p>Stands for the number of machine modes available on the target

  636. machine.  This is one greater than the largest numeric value of any

  637. machine mode.

  638. </p>

  639. <a name="index-GET_005fMODE_005fNAME"></a>

  640. </dd>

  641. <dt><code>GET_MODE_NAME (<var>m</var>)</code></dt>

  642. <dd><p>Returns the name of mode <var>m</var> as a string.

  643. </p>

  644. <a name="index-GET_005fMODE_005fCLASS"></a>

  645. </dd>

  646. <dt><code>GET_MODE_CLASS (<var>m</var>)</code></dt>

  647. <dd><p>Returns the mode class of mode <var>m</var>.

  648. </p>

  649. <a name="index-GET_005fMODE_005fWIDER_005fMODE"></a>

  650. </dd>

  651. <dt><code>GET_MODE_WIDER_MODE (<var>m</var>)</code></dt>

  652. <dd><p>Returns the next wider natural mode.  For example, the expression

  653. <code>GET_MODE_WIDER_MODE (QImode)</code> returns <code>HImode</code>.

  654. </p>

  655. <a name="index-GET_005fMODE_005fSIZE"></a>

  656. </dd>

  657. <dt><code>GET_MODE_SIZE (<var>m</var>)</code></dt>

  658. <dd><p>Returns the size in bytes of a datum of mode <var>m</var>.

  659. </p>

  660. <a name="index-GET_005fMODE_005fBITSIZE"></a>

  661. </dd>

  662. <dt><code>GET_MODE_BITSIZE (<var>m</var>)</code></dt>

  663. <dd><p>Returns the size in bits of a datum of mode <var>m</var>.

  664. </p>

  665. <a name="index-GET_005fMODE_005fIBIT"></a>

  666. </dd>

  667. <dt><code>GET_MODE_IBIT (<var>m</var>)</code></dt>

  668. <dd><p>Returns the number of integral bits of a datum of fixed-point mode <var>m</var>.

  669. </p>

  670. <a name="index-GET_005fMODE_005fFBIT"></a>

  671. </dd>

  672. <dt><code>GET_MODE_FBIT (<var>m</var>)</code></dt>

  673. <dd><p>Returns the number of fractional bits of a datum of fixed-point mode <var>m</var>.

  674. </p>

  675. <a name="index-GET_005fMODE_005fMASK"></a>

  676. </dd>

  677. <dt><code>GET_MODE_MASK (<var>m</var>)</code></dt>

  678. <dd><p>Returns a bitmask containing 1 for all bits in a word that fit within

  679. mode <var>m</var>.  This macro can only be used for modes whose bitsize is

  680. less than or equal to <code>HOST_BITS_PER_INT</code>.

  681. </p>

  682. <a name="index-GET_005fMODE_005fALIGNMENT"></a>

  683. </dd>

  684. <dt><code>GET_MODE_ALIGNMENT (<var>m</var>)</code></dt>

  685. <dd><p>Return the required alignment, in bits, for an object of mode <var>m</var>.

  686. </p>

  687. <a name="index-GET_005fMODE_005fUNIT_005fSIZE"></a>

  688. </dd>

  689. <dt><code>GET_MODE_UNIT_SIZE (<var>m</var>)</code></dt>

  690. <dd><p>Returns the size in bytes of the subunits of a datum of mode <var>m</var>.

  691. This is the same as <code>GET_MODE_SIZE</code> except in the case of complex

  692. modes.  For them, the unit size is the size of the real or imaginary

  693. part.

  694. </p>

  695. <a name="index-GET_005fMODE_005fNUNITS"></a>

  696. </dd>

  697. <dt><code>GET_MODE_NUNITS (<var>m</var>)</code></dt>

  698. <dd><p>Returns the number of units contained in a mode, i.e.,

  699. <code>GET_MODE_SIZE</code> divided by <code>GET_MODE_UNIT_SIZE</code>.

  700. </p>

  701. <a name="index-GET_005fCLASS_005fNARROWEST_005fMODE"></a>

  702. </dd>

  703. <dt><code>GET_CLASS_NARROWEST_MODE (<var>c</var>)</code></dt>

  704. <dd><p>Returns the narrowest mode in mode class <var>c</var>.

  705. </p></dd>

  706. </dl>

  707. 

  708. <p>The following 3 variables are defined on every target.   They can be

  709. used to allocate buffers that are guaranteed to be large enough to

  710. hold any value that can be represented on the target.   The first two

  711. can be overridden by defining them in the target&rsquo;s mode.def file,

  712. however, the value must be a constant that can determined very early

  713. in the compilation process.   The third symbol cannot be overridden.

  714. </p>

  715. <dl compact="compact">

  716. <dd><a name="index-BITS_005fPER_005fUNIT"></a>

  717. </dd>

  718. <dt><code>BITS_PER_UNIT</code></dt>

  719. <dd><p>The number of bits in an addressable storage unit (byte).  If you do

  720. not define this, the default is 8.

  721. </p>

  722. <a name="index-MAX_005fBITSIZE_005fMODE_005fANY_005fINT"></a>

  723. </dd>

  724. <dt><code>MAX_BITSIZE_MODE_ANY_INT</code></dt>

  725. <dd><p>The maximum bitsize of any mode that is used in integer math.  This

  726. should be overridden by the target if it uses large integers as

  727. containers for larger vectors but otherwise never uses the contents to

  728. compute integer values.

  729. </p>

  730. <a name="index-MAX_005fBITSIZE_005fMODE_005fANY_005fMODE"></a>

  731. </dd>

  732. <dt><code>MAX_BITSIZE_MODE_ANY_MODE</code></dt>

  733. <dd><p>The bitsize of the largest mode on the target.  The default value is

  734. the largest mode size given in the mode definition file, which is

  735. always correct for targets whose modes have a fixed size.  Targets

  736. that might increase the size of a mode beyond this default should define

  737. <code>MAX_BITSIZE_MODE_ANY_MODE</code> to the actual upper limit in

  738. <samp><var>machine</var>-modes.def</samp>.

  739. </p></dd>

  740. </dl>

  741. 

  742. <a name="index-byte_005fmode"></a>

  743. <a name="index-word_005fmode"></a>

  744. <p>The global variables <code>byte_mode</code> and <code>word_mode</code> contain modes

  745. whose classes are <code>MODE_INT</code> and whose bitsizes are either

  746. <code>BITS_PER_UNIT</code> or <code>BITS_PER_WORD</code>, respectively.  On 32-bit

  747. machines, these are <code>QImode</code> and <code>SImode</code>, respectively.

  748. </p>

  749. <hr>

  750. <div class="header">

  751. <p>

  752. Next: <a href="Constants.html#Constants" accesskey="n" rel="next">Constants</a>, Previous: <a href="Flags.html#Flags" accesskey="p" rel="prev">Flags</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>

  753. </div>

  754. 

  755. 

  756. 

  757. </body>

  758. </html>