lib/fenv-round.c

   1 /* Functions for controlling the floating-point rounding direction.
   2    Copyright (C) 1997-2025 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Based on glibc/sysdeps/<cpu>/{fegetround.c,fesetround.c}
  18    together with glibc/sysdeps/<cpu>/{fpu_control.h,fenv_private.h,fenv_libc.h}.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include <fenv.h>
  24
  25 #include "fenv-private.h"
  26
  27 #if defined __GNUC__ || defined __clang__ || defined _MSC_VER
  28
  29 # if (defined __x86_64__ || defined _M_X64) || (defined __i386 || defined _M_IX86)
  30
  31 int
  32 fegetround (void)
  33 {
  34 #  ifdef _MSC_VER
  35   /* Use the rounding direction from the SSE unit.  */
  36   unsigned int mxcsr;
  37   _FPU_GETSSECW (mxcsr);
  38   unsigned int fctrl = (mxcsr >> 3) & 0x0C00;
  39 #  else
  40   /* Use the rounding direction from the control word of the 387 unit, the
  41      so-called fctrl register.
  42      The rounding direction of the SSE unit, in the mxcsr register, is expected
  43      to be in sync with that.  */
  44   unsigned short fctrl;
  45   _FPU_GETCW (fctrl);
  46 #  endif
  47 #  ifdef _MSC_VER
  48   /* The MSVC header files have different values for the rounding directions
  49      than all the other platforms, and the even changed between MSVC 14 and
  50      MSVC 14.30 (!).  Map
  51        0x0000 -> FE_TONEAREST = 0
  52        0x0400 -> FE_DOWNWARD
  53        0x0800 -> FE_UPWARD
  54        0x0C00 -> FE_TOWARDZERO = FE_DOWNWARD | FE_UPWARD */
  55   return (fctrl & 0x0800 ? FE_UPWARD : 0) | (fctrl & 0x0400 ? FE_DOWNWARD : 0);
  56 #  else
  57   return fctrl & 0x0C00;
  58 #  endif
  59 }
  60
  61 int
  62 fesetround (int rounding_direction)
  63 {
  64 #  ifdef _MSC_VER
  65   /* The MSVC header files have different values for the rounding directions
  66      than all the other platforms.  */
  67   if ((rounding_direction & ~0x0300) != 0)
  68     return -1;
  69   /* The MSVC header files have different values for the rounding directions
  70      than all the other platforms, and the even changed between MSVC 14 and
  71      MSVC 14.30 (!).  Map
  72      FE_TONEAREST = 0                        -> 0x0000
  73      FE_DOWNWARD                             -> 0x0400
  74      FE_UPWARD                               -> 0x0800
  75      FE_TOWARDZERO = FE_DOWNWARD | FE_UPWARD -> 0x0C00  */
  76   rounding_direction =
  77     (rounding_direction & FE_UPWARD ? 0x0800 : 0)
  78     | (rounding_direction & FE_DOWNWARD ? 0x0400 : 0);
  79 #  else
  80   if ((rounding_direction & ~0x0C00) != 0)
  81     return -1;
  82 #  endif
  83
  84 #  ifdef _MSC_VER
  85   /* Set it in the SSE unit.  */
  86   unsigned int mxcsr, orig_mxcsr;
  87   _FPU_GETSSECW (orig_mxcsr);
  88   mxcsr = (orig_mxcsr & ~(0x0C00 << 3)) | (rounding_direction << 3);
  89   if (mxcsr != orig_mxcsr)
  90     _FPU_SETSSECW (mxcsr);
  91 #  else
  92   /* Set it in the 387 unit.  */
  93   unsigned short fctrl, orig_fctrl;
  94   _FPU_GETCW (orig_fctrl);
  95   fctrl = (orig_fctrl & ~0x0C00) | rounding_direction;
  96   if (fctrl != orig_fctrl)
  97     _FPU_SETCW (fctrl);
  98
  99   if (CPU_HAS_SSE ())
 100     {
 101       /* Set it in the SSE unit as well.  */
 102       unsigned int mxcsr, orig_mxcsr;
 103       _FPU_GETSSECW (orig_mxcsr);
 104       mxcsr = (orig_mxcsr & ~(0x0C00 << 3)) | (rounding_direction << 3);
 105       if (mxcsr != orig_mxcsr)
 106         _FPU_SETSSECW (mxcsr);
 107     }
 108 #  endif
 109
 110   return 0;
 111 }
 112
 113 # elif defined __aarch64__ /* arm64 */
 114
 115 int
 116 fegetround (void)
 117 {
 118   unsigned long fpcr;
 119   _FPU_GETCW (fpcr);
 120   return (fpcr & 0x00C00000UL)
 121 #  if FE_TOWARDZERO == 3 /* FreeBSD compatible FE_* values */
 122          >> 22
 123 #  endif
 124          ;
 125 }
 126
 127 int
 128 fesetround (int rounding_direction)
 129 {
 130 #  if FE_TOWARDZERO == 3 /* FreeBSD compatible FE_* values */
 131   if ((rounding_direction & ~3) != 0)
 132     return -1;
 133   rounding_direction = rounding_direction << 22;
 134 #  else /* glibc compatible FE_* values */
 135   if ((rounding_direction & ~0x00C00000UL) != 0)
 136     return -1;
 137 #  endif
 138   unsigned long fpcr, orig_fpcr;
 139   _FPU_GETCW (orig_fpcr);
 140   fpcr = (orig_fpcr & ~0x00C00000UL) | rounding_direction;
 141   if (fpcr != orig_fpcr)
 142     _FPU_SETCW (fpcr);
 143   return 0;
 144 }
 145
 146 # elif defined __arm__
 147
 148 int
 149 fegetround (void)
 150 {
 151 #  ifdef __SOFTFP__
 152   return FE_TONEAREST;
 153 #  else
 154   unsigned int fpscr;
 155   _FPU_GETCW (fpscr);
 156   return fpscr & 0x00C00000U;
 157 #  endif
 158 }
 159
 160 int
 161 fesetround (int rounding_direction)
 162 {
 163 #  ifdef __SOFTFP__
 164   if (rounding_direction != FE_TONEAREST)
 165     return -1;
 166 #  else
 167   if ((rounding_direction & ~0x00C00000U) != 0)
 168     return -1;
 169   unsigned int fpscr, orig_fpscr;
 170   _FPU_GETCW (orig_fpscr);
 171   fpscr = (orig_fpscr & ~0x00C00000U) | rounding_direction;
 172   if (fpscr != orig_fpscr)
 173     _FPU_SETCW (fpscr);
 174 #  endif
 175   return 0;
 176 }
 177
 178 # elif defined __alpha
 179
 180 int
 181 fegetround (void)
 182 {
 183   unsigned long fpcr;
 184   _FPU_GETCW (fpcr);
 185   return (fpcr >> 58) & 0x3UL;
 186 }
 187
 188 int
 189 fesetround (int rounding_direction)
 190 {
 191   if ((rounding_direction & ~0x3UL) != 0)
 192     return -1;
 193   unsigned long fpcr, orig_fpcr;
 194   _FPU_GETCW (orig_fpcr);
 195   fpcr = (orig_fpcr & ~(0x3UL << 58))
 196          | ((unsigned long) rounding_direction << 58);
 197   if (fpcr != orig_fpcr)
 198     _FPU_SETCW (fpcr);
 199   return 0;
 200 }
 201
 202 # elif defined __hppa
 203
 204 int
 205 fegetround (void)
 206 {
 207   unsigned int fpstatus;
 208   _FPU_GETCW (fpstatus);
 209   return fpstatus & 0x00000600U;
 210 }
 211
 212 int
 213 fesetround (int rounding_direction)
 214 {
 215   if ((rounding_direction & ~0x00000600U) != 0)
 216     return -1;
 217   unsigned int fpstatus, orig_fpstatus;
 218   _FPU_GETCW (orig_fpstatus);
 219   fpstatus = (orig_fpstatus & ~0x00000600U) | rounding_direction;
 220   if (fpstatus != orig_fpstatus)
 221     _FPU_SETCW (fpstatus);
 222   return 0;
 223 }
 224
 225 # elif defined __ia64__
 226
 227 int
 228 fegetround (void)
 229 {
 230   unsigned long fpsr;
 231   _FPU_GETCW (fpsr);
 232   return (fpsr >> 10) & 0x3UL;
 233 }
 234
 235 int
 236 fesetround (int rounding_direction)
 237 {
 238   if ((rounding_direction & ~0x3UL) != 0)
 239     return -1;
 240   unsigned long fpsr, orig_fpsr;
 241   _FPU_GETCW (orig_fpsr);
 242   fpsr = (orig_fpsr & ~(0x3UL << 10))
 243          | ((unsigned long) rounding_direction << 10);
 244   if (fpsr != orig_fpsr)
 245     _FPU_SETCW (fpsr);
 246   return 0;
 247 }
 248
 249 # elif defined __m68k__
 250
 251 int
 252 fegetround (void)
 253 {
 254   unsigned int fpcr;
 255   _FPU_GETCW (fpcr);
 256   return fpcr & 0x30U;
 257 }
 258
 259 int
 260 fesetround (int rounding_direction)
 261 {
 262   if ((rounding_direction & ~0x30U) != 0)
 263     return -1;
 264   unsigned int fpcr, orig_fpcr;
 265   _FPU_GETCW (orig_fpcr);
 266   fpcr = (orig_fpcr & ~0x30U) | rounding_direction;
 267   if (fpcr != orig_fpcr)
 268     _FPU_SETCW (fpcr);
 269   return 0;
 270 }
 271
 272 # elif defined __mips__
 273
 274 int
 275 fegetround (void)
 276 {
 277   unsigned int fcsr;
 278   _FPU_GETCW (fcsr);
 279   return fcsr & 0x3U;
 280 }
 281
 282 int
 283 fesetround (int rounding_direction)
 284 {
 285   if ((rounding_direction & ~0x3U) != 0)
 286     return -1;
 287   unsigned int fcsr, orig_fcsr;
 288   _FPU_GETCW (orig_fcsr);
 289   fcsr = (orig_fcsr & ~0x3U) | rounding_direction;
 290   if (fcsr != orig_fcsr)
 291     _FPU_SETCW (fcsr);
 292   return 0;
 293 }
 294
 295 # elif defined __loongarch__
 296
 297 int
 298 fegetround (void)
 299 {
 300   unsigned int fcsr;
 301   _FPU_GETCW (fcsr);
 302   return fcsr & 0x300U;
 303 }
 304
 305 int
 306 fesetround (int rounding_direction)
 307 {
 308   if ((rounding_direction & ~0x300U) != 0)
 309     return -1;
 310   unsigned int fcsr, orig_fcsr;
 311   _FPU_GETCW (orig_fcsr);
 312   fcsr = (orig_fcsr & ~0x300U) | rounding_direction;
 313   if (fcsr != orig_fcsr)
 314     _FPU_SETCW (fcsr);
 315   return 0;
 316 }
 317
 318 # elif defined __powerpc__
 319
 320 /* The AIX header files have different values for the rounding directions
 321    than all the other platforms: The values 0 and 1 are swapped.
 322    (They probably did this in order to have a trivial FLT_ROUNDS macro, cf.
 323    <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/float.h.html>.)
 324    Define some handy macros for conversion.  */
 325 #  ifdef _AIX
 326 #   define fe_to_hardware(x) ((x) ^ ((x) < 2))
 327 #   define hardware_to_fe(x) ((x) ^ ((x) < 2))
 328 #  else
 329 #   define fe_to_hardware(x) (x)
 330 #   define hardware_to_fe(x) (x)
 331 #  endif
 332
 333 int
 334 fegetround (void)
 335 {
 336 #  if 1
 337   unsigned int result;
 338   __asm__ __volatile__ ("mcrfs 7,7 ; mfcr %0" : "=r" (result) : : "cr7");
 339   return hardware_to_fe (result & 3);
 340 #  else
 341   union { unsigned long long u; double f; } memenv;
 342   _FPU_GETCW_AS_DOUBLE (memenv.f);
 343   return hardware_to_fe (memenv.u & 3);
 344 #  endif
 345 }
 346
 347 int
 348 fesetround (int rounding_direction)
 349 {
 350   if ((rounding_direction & ~0x3U) != 0)
 351     return -1;
 352 #  ifdef _AIX
 353   rounding_direction = fe_to_hardware (rounding_direction);
 354 #  endif
 355   if (rounding_direction & 2)
 356     __asm__ __volatile__ ("mtfsb1 30");
 357   else
 358     __asm__ __volatile__ ("mtfsb0 30");
 359   if (rounding_direction & 1)
 360     __asm__ __volatile__ ("mtfsb1 31");
 361   else
 362     __asm__ __volatile__ ("mtfsb0 31");
 363   return 0;
 364 }
 365
 366 # elif defined __riscv
 367
 368 int
 369 fegetround (void)
 370 {
 371   int rounding_direction;
 372   __asm__ __volatile__ ("frrm %0" : "=r" (rounding_direction));
 373 #  if FE_UPWARD == 0x60 /* FreeBSD compatible FE_* values */
 374   return rounding_direction << 5;
 375 #  else
 376   return rounding_direction;
 377 #  endif
 378 }
 379
 380 int
 381 fesetround (int rounding_direction)
 382 {
 383 #  if FE_UPWARD == 0x60 /* FreeBSD compatible FE_* values */
 384   if ((rounding_direction & ~0x60) != 0)
 385     return -1;
 386   rounding_direction = rounding_direction >> 5;
 387 #  else
 388   if ((rounding_direction & ~3) != 0)
 389     return -1;
 390 #  endif
 391   __asm__ __volatile__ ("fsrm %z0" : : "rJ" (rounding_direction));
 392   return 0;
 393 }
 394
 395 # elif defined __s390__ || defined __s390x__
 396
 397 int
 398 fegetround (void)
 399 {
 400   unsigned int fpc;
 401   _FPU_GETCW (fpc);
 402   return fpc & 0x3U;
 403 }
 404
 405 int
 406 fesetround (int rounding_direction)
 407 {
 408   if ((rounding_direction & ~0x3U) != 0)
 409     return -1;
 410 #  if 1
 411   __asm__ __volatile__ ("srnm 0(%0)" : : "a" (rounding_direction));
 412 #  else
 413   unsigned int fpc, orig_fpc;
 414   _FPU_GETCW (orig_fpc);
 415   fpc = (orig_fpc & ~0x3U) | rounding_direction;
 416   if (fpc != orig_fpc)
 417     _FPU_SETCW (fpc);
 418 #  endif
 419   return 0;
 420 }
 421
 422 # elif defined __sh__
 423
 424 int
 425 fegetround (void)
 426 {
 427   unsigned int fpscr;
 428   _FPU_GETCW (fpscr);
 429   return fpscr & 0x1U;
 430 }
 431
 432 int
 433 fesetround (int rounding_direction)
 434 {
 435   if ((rounding_direction & ~0x1U) != 0)
 436     return -1;
 437   unsigned int fpscr, orig_fpscr;
 438   _FPU_GETCW (orig_fpscr);
 439   fpscr = (orig_fpscr & ~0x1U) | rounding_direction;
 440   if (fpscr != orig_fpscr)
 441     _FPU_SETCW (fpscr);
 442   return 0;
 443 }
 444
 445 # elif defined __sparc
 446
 447 int
 448 fegetround (void)
 449 {
 450   unsigned long fsr;
 451   _FPU_GETCW (fsr);
 452   return (fsr & 0xC0000000UL)
 453 #  if FE_DOWNWARD == 3 /* FreeBSD compatible FE_* values */
 454          >> 30
 455 #  endif
 456          ;
 457 }
 458
 459 int
 460 fesetround (int rounding_direction)
 461 {
 462 #  if FE_DOWNWARD == 3 /* FreeBSD compatible FE_* values */
 463   if ((rounding_direction & ~3) != 0)
 464     return -1;
 465   rounding_direction = (unsigned int) rounding_direction << 30;
 466 #  else /* glibc compatible FE_* values */
 467   if (((unsigned int) rounding_direction & ~0xC0000000UL) != 0)
 468     return -1;
 469 #  endif
 470   unsigned long fsr, orig_fsr;
 471   _FPU_GETCW (orig_fsr);
 472   fsr = (orig_fsr & ~0xC0000000UL) | (unsigned int) rounding_direction;
 473   if (fsr != orig_fsr)
 474     _FPU_SETCW (fsr);
 475   return 0;
 476 }
 477
 478 # else
 479
 480 #  if defined __GNUC__ || defined __clang__
 481 #   warning "Unknown CPU / architecture. Please report your platform and compiler to <bug-gnulib@gnu.org>."
 482 #  endif
 483 #  define NEED_FALLBACK 1
 484
 485 # endif
 486
 487 #else
 488
 489 /* The compiler does not support __asm__ statements or equivalent
 490    intrinsics.  */
 491
 492 # if HAVE_FPSETROUND
 493 /* FreeBSD ≥ 3.1, NetBSD ≥ 1.1, OpenBSD, IRIX, Solaris, Minix ≥ 3.2.  */
 494
 495 /* Get fpgetround, fpsetround.  */
 496 #  include <ieeefp.h>
 497
 498 int
 499 fegetround (void)
 500 {
 501   return fpgetround ();
 502 }
 503
 504 int
 505 fesetround (int rounding_direction)
 506 {
 507   fpsetround (rounding_direction);
 508   return 0;
 509 }
 510
 511 # elif defined _AIX /* AIX */
 512
 513 /* Get fp_read_rnd, fp_swap_rnd.  */
 514 #  include <float.h>
 515
 516 /* Documentation:
 517    <https://www.ibm.com/docs/en/aix/7.3?topic=f-fp-read-rnd-fp-swap-rnd-subroutine>  */
 518
 519 int
 520 fegetround (void)
 521 {
 522   return fp_read_rnd ();
 523 }
 524
 525 int
 526 fesetround (int rounding_direction)
 527 {
 528   fp_swap_rnd (rounding_direction);
 529   return 0;
 530 }
 531
 532 # else
 533
 534 #  define NEED_FALLBACK 1
 535
 536 # endif
 537
 538 #endif
 539
 540 #if NEED_FALLBACK
 541
 542 /* A dummy fallback.  */
 543
 544 # include <float.h>
 545 # include <stdlib.h>
 546
 547 int
 548 fegetround (void)
 549 {
 550   /* Cf. <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/float.h.html> */
 551   switch (FLT_ROUNDS)
 552     {
 553     case 0: return FE_TOWARDZERO;
 554     case 1: return FE_TONEAREST;
 555     case 2: return FE_UPWARD;
 556     case 3: return FE_DOWNWARD;
 557     default: abort ();
 558     }
 559 }
 560
 561 int
 562 fesetround (int rounding_direction)
 563 {
 564   if (rounding_direction != fegetround ())
 565     return -1;
 566   return 0;
 567 }
 568
 569 #endif