lib/fenv-except-state-set.c

   1 /* Functions for saving the floating-point exception status flags.
   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>/{fgetexcptflg.c,fsetexcptflg.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 /* On most OSes, fexcept_t is binary-equivalent to an 'unsigned short'.
  32    On NetBSD, OpenBSD, Solaris, Cygwin, MSVC, Android/x86_64, Minix, fexcept_t
  33    is equivalent to an 'unsigned int'.
  34    A simple C cast does the necessary conversion.  */
  35
  36 int
  37 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
  38 {
  39   exceptions &= FE_ALL_EXCEPT;
  40
  41   unsigned int desired_flags = (unsigned int) *saved_flags;
  42
  43 #  if defined _MSC_VER
  44   exceptions = exceptions_to_x86hardware (exceptions);
  45   desired_flags = exceptions_to_x86hardware (desired_flags);
  46
  47   /* Modify the flags in the SSE unit.  */
  48   unsigned int mxcsr, orig_mxcsr;
  49   _FPU_GETSSECW (orig_mxcsr);
  50   mxcsr = orig_mxcsr ^ ((orig_mxcsr ^ desired_flags) & exceptions);
  51   if (mxcsr != orig_mxcsr)
  52     _FPU_SETSSECW (mxcsr);
  53
  54 #  else
  55
  56   /* The flags can be set in the 387 unit or in the SSE unit.
  57      When we need to clear a flag, we need to do so in both units,
  58      due to the way fetestexcept() is implemented.
  59      When we need to set a flag, it is sufficient to do it in the SSE unit,
  60      because that is guaranteed to not trap.  However, on i386 CPUs that have
  61      only a 387 unit, set the flags in the 387, as long as this cannot trap.  */
  62
  63   if (CPU_HAS_SSE ())
  64     {
  65       /* Modify the flags in the SSE unit.  */
  66       unsigned int mxcsr, orig_mxcsr;
  67       _FPU_GETSSECW (orig_mxcsr);
  68       mxcsr = orig_mxcsr ^ ((orig_mxcsr ^ desired_flags) & exceptions);
  69       if (mxcsr != orig_mxcsr)
  70         _FPU_SETSSECW (mxcsr);
  71
  72       /* Modify the flags in the 387 unit, but only by clearing bits, not by
  73          setting bits.  */
  74       x86_387_fenv_t env;
  75       __asm__ __volatile__ ("fnstenv %0" : "=m" (*&env));
  76       /* Note: fnstenv masks all floating-point exceptions until the fldenv
  77          below.  */
  78       env.__status_word &= ~ (exceptions & ~desired_flags);
  79       __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
  80     }
  81 #   if !(defined __x86_64__ || defined _M_X64)
  82   else
  83     {
  84       /* Modify the flags in the 387 unit.  */
  85       x86_387_fenv_t env;
  86       __asm__ __volatile__ ("fnstenv %0" : "=m" (*&env));
  87       /* Note: fnstenv masks all floating-point exceptions until the fldenv
  88          or fldcw below.  */
  89       env.__status_word ^= ((env.__status_word ^ desired_flags) & exceptions);
  90       if ((~env.__control_word) & env.__status_word & exceptions)
  91         {
  92           /* Setting the exception flags may trigger a trap (at the next
  93              floating-point instruction, but that does not matter).
  94              ISO C 23 § 7.6.4.5 does not allow it.  */
  95           __asm__ __volatile__ ("fldcw %0" : : "m" (*&env.__control_word));
  96           return -1;
  97         }
  98       __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
  99     }
 100 #   endif
 101 #  endif
 102   return 0;
 103 }
 104
 105 # elif defined __aarch64__ /* arm64 */
 106
 107 /* On Linux, NetBSD, and Android, fexcept_t is binary-equivalent to
 108    an 'unsigned int'.
 109    On macOS, fexcept_t is binary-equivalent to an 'unsigned short'.
 110    On FreeBSD and OpenBSD, fexcept_t is binary-equivalent to an 'unsigned long'.
 111    A simple C cast does the necessary conversion.  */
 112
 113 int
 114 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 115 {
 116   unsigned long desired_flags = (unsigned long) *saved_flags;
 117   unsigned long fpsr, orig_fpsr;
 118   _FPU_GETFPSR (orig_fpsr);
 119   fpsr = orig_fpsr ^ ((orig_fpsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 120   if (fpsr != orig_fpsr)
 121     _FPU_SETFPSR (fpsr);
 122   /* Possibly some new exception flags have been set.  But just storing them
 123      does not cause a trap to be executed (when traps are enabled).  */
 124   return 0;
 125 }
 126
 127 # elif defined __arm__
 128
 129 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 130
 131 int
 132 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 133 {
 134 #  ifdef __SOFTFP__
 135   if (exceptions != 0)
 136     return -1;
 137 #  else
 138   unsigned int desired_flags = (unsigned int) *saved_flags;
 139   unsigned int fpscr, orig_fpscr;
 140   _FPU_GETCW (orig_fpscr);
 141   fpscr = orig_fpscr ^ ((orig_fpscr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 142   if (fpscr != orig_fpscr)
 143     _FPU_SETCW (fpscr);
 144 #  endif
 145   return 0;
 146 }
 147
 148 # elif defined __alpha
 149
 150 /* On all OSes except NetBSD and OpenBSD, fexcept_t is binary-equivalent to
 151    an 'unsigned long'.
 152    On NetBSD, it is equivalent to an 'unsigned short'.
 153    On OpenBSD, it is equivalent to an 'unsigned int'.
 154    A simple C cast does the necessary conversion.  */
 155
 156 int
 157 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 158 {
 159   unsigned long desired_flags = (unsigned long) *saved_flags;
 160   unsigned long swcr, orig_swcr;
 161   orig_swcr = __ieee_get_fp_control ();
 162   swcr = orig_swcr ^ ((orig_swcr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 163   if (swcr != orig_swcr)
 164     __ieee_set_fp_control (swcr);
 165   /* Possibly some new exception flags have been set.  But just storing them
 166      does not cause a trap to be executed (when traps are enabled).  */
 167   return 0;
 168 }
 169
 170 # elif defined __hppa
 171
 172 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 173
 174 int
 175 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 176 {
 177   unsigned int desired_flags = (unsigned int) *saved_flags;
 178   union { unsigned long long fpreg; unsigned int halfreg[2]; } s;
 179   /* Get the current status word. */
 180   __asm__ __volatile__ ("fstd %%fr0,0(%1)" : "=m" (s.fpreg) : "r" (&s.fpreg) : "%r0");
 181   unsigned int old_halfreg0 = s.halfreg[0];
 182   /* Modify all the relevant bits. */
 183   s.halfreg[0] ^= (s.halfreg[0] ^ (desired_flags << 27)) & ((FE_ALL_EXCEPT & exceptions) << 27);
 184   if (s.halfreg[0] != old_halfreg0)
 185     {
 186       /* Store the new status word.  */
 187       __asm__ __volatile__ ("fldd 0(%0),%%fr0" : : "r" (&s.fpreg), "m" (s.fpreg) : "%r0");
 188     }
 189   /* Possibly some new exception flags have been set.  But just storing them
 190      does not cause a trap to be executed (when traps are enabled).  */
 191   return 0;
 192 }
 193
 194 # elif defined __ia64__
 195
 196 /* On all OSes except NetBSD, fexcept_t is binary-equivalent to
 197    an 'unsigned long'.
 198    On NetBSD, it is equivalent to an 'unsigned short'.
 199    A simple C cast does the necessary conversion.  */
 200
 201 int
 202 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 203 {
 204   unsigned long desired_flags = (unsigned long) *saved_flags;
 205   unsigned long fpsr, orig_fpsr;
 206   _FPU_GETCW (orig_fpsr);
 207   fpsr = orig_fpsr ^ ((orig_fpsr ^ (desired_flags << 13)) & ((FE_ALL_EXCEPT & exceptions) << 13));
 208   if (fpsr != orig_fpsr)
 209     _FPU_SETCW (fpsr);
 210   /* Possibly some new exception flags have been set.  But just storing them
 211      does not cause a trap to be executed (when traps are enabled).  */
 212   return 0;
 213 }
 214
 215 # elif defined __m68k__
 216
 217 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 218
 219 int
 220 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 221 {
 222   unsigned int desired_flags = (unsigned int) *saved_flags;
 223   unsigned int fpsr, orig_fpsr;
 224   _FPU_GETFPSR (orig_fpsr);
 225   fpsr = orig_fpsr ^ ((orig_fpsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 226   if (fpsr != orig_fpsr)
 227     _FPU_SETFPSR (fpsr);
 228   /* Possibly some new exception flags have been set.  But just storing them
 229      does not cause a trap to be executed (when traps are enabled).  */
 230   return 0;
 231 }
 232
 233 # elif defined __mips__
 234
 235 /* On all OSes except NetBSD and OpenBSD, fexcept_t is binary-equivalent to
 236    an 'unsigned short'.
 237    On NetBSD and OpenBSD, it is equivalent to an 'unsigned int'.
 238    A simple C cast does the necessary conversion.  */
 239
 240 int
 241 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 242 {
 243   unsigned int desired_flags = (unsigned int) *saved_flags;
 244   unsigned int fcsr, orig_fcsr;
 245   _FPU_GETCW (orig_fcsr);
 246   fcsr = orig_fcsr ^ ((orig_fcsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 247   if (fcsr != orig_fcsr)
 248     _FPU_SETCW (fcsr);
 249   return 0;
 250 }
 251
 252 # elif defined __loongarch__
 253
 254 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 255
 256 int
 257 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 258 {
 259   unsigned int desired_flags = (unsigned int) *saved_flags;
 260   unsigned int fcsr, orig_fcsr;
 261   _FPU_GETCW (orig_fcsr);
 262   fcsr = orig_fcsr ^ ((orig_fcsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 263   if (fcsr != orig_fcsr)
 264     _FPU_SETCW (fcsr);
 265   /* Possibly some new exception flags have been set.  But just storing them
 266      does not cause a trap to be executed (when traps are enabled).  */
 267   return 0;
 268 }
 269
 270 # elif defined __powerpc__
 271
 272 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 273
 274 int
 275 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 276 {
 277   /* The hardware does not support setting an exception flag without triggering
 278      a trap, except through the "Ignore Exceptions Mode", bits FE0 and FE1 of
 279      the MSR register set to zero, that can be obtained through a system call:
 280        - On Linux and NetBSD: prctl (PR_SET_FPEXC, PR_FP_EXC_DISABLED);
 281        - On AIX: fp_trap (FP_TRAP_OFF);
 282      But that is not what we need here, as it would have a persistent effect on
 283      the thread.  */
 284   exceptions &= FE_ALL_EXCEPT;
 285
 286   unsigned int desired_flags = (unsigned int) *saved_flags;
 287   desired_flags &= exceptions;
 288
 289   union { unsigned long long u; double f; } memenv, orig_memenv;
 290   _FPU_GETCW_AS_DOUBLE (memenv.f);
 291   orig_memenv = memenv;
 292
 293   /* Instead of clearing FE_INVALID (= bit 29), we need to clear the
 294      individual bits.  */
 295   memenv.u &= ~ (exceptions & FE_INVALID
 296                  ? (exceptions & ~FE_INVALID) | 0x01F80700U
 297                  : exceptions);
 298   /* Instead of setting FE_INVALID (= bit 29), we need to set one of the
 299      individual bits: bit 10 or, if that does not work, bit 24.  */
 300   memenv.u |= (desired_flags & FE_INVALID
 301                ? (desired_flags & ~FE_INVALID) | (1U << 10)
 302                : desired_flags);
 303
 304   if (!(memenv.u == orig_memenv.u))
 305     {
 306       if (memenv.u & (exceptions >> 22))
 307         {
 308           /* Setting the exception flags may trigger a trap.
 309              ISO C 23 § 7.6.4.5 does not allow it.  */
 310           return -1;
 311         }
 312       _FPU_SETCW_AS_DOUBLE (memenv.f);
 313       if (desired_flags & FE_INVALID)
 314         {
 315           /* Did it work?  */
 316           _FPU_GETCW_AS_DOUBLE (memenv.f);
 317           if ((memenv.u & FE_INVALID) == 0)
 318             {
 319               memenv.u |= (1U << 24);
 320               _FPU_SETCW_AS_DOUBLE (memenv.f);
 321             }
 322         }
 323     }
 324
 325   return 0;
 326 }
 327
 328 # elif defined __riscv
 329
 330 /* On all OSes except FreeBSD, fexcept_t is binary-equivalent to
 331    an 'unsigned int'.
 332    On FreeBSD, it is equivalent to an 'unsigned long'.
 333    A simple C cast does the necessary conversion.  */
 334
 335 int
 336 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 337 {
 338 #  if 1 /* both should be equivalent */
 339   exceptions &= FE_ALL_EXCEPT;
 340
 341   unsigned int desired_flags = (unsigned int) *saved_flags;
 342   desired_flags &= exceptions;
 343
 344   __asm__ __volatile__ ("csrc fflags, %0" : : "r" (exceptions));
 345   __asm__ __volatile__ ("csrs fflags, %0" : : "r" (desired_flags));
 346 #  else
 347   unsigned int desired_flags = (unsigned int) *saved_flags;
 348   unsigned int fcsr, orig_fcsr;
 349   __asm__ __volatile__ ("frflags %0" : "=r" (orig_fcsr)); /* same as "csrr %0, fflags" */
 350   fcsr = orig_fcsr ^ ((orig_fcsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 351   if (fcsr != orig_fcsr)
 352     __asm__ __volatile__ ("fsflags %0" : : "r" (fcsr)); /* same as "csrw fflags, %0" */
 353 #  endif
 354
 355   return 0;
 356 }
 357
 358 # elif defined __s390__ || defined __s390x__
 359
 360 /* On all OSes, fexcept_t is binary-equivalent to an 'unsigned int'.  */
 361
 362 int
 363 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 364 {
 365   unsigned int desired_flags = (unsigned int) *saved_flags;
 366   unsigned int fpc, orig_fpc;
 367   _FPU_GETCW (orig_fpc);
 368 #  if FE_INEXACT == 8 /* glibc compatible FE_* values */
 369   fpc = orig_fpc ^ ((orig_fpc ^ (desired_flags << 16)) & ((FE_ALL_EXCEPT & exceptions) << 16));
 370   if ((fpc & 0x00000300) == 0)
 371     /* Clear the corresponding bits of the "data exception code".  */
 372     fpc &= ~((FE_ALL_EXCEPT & exceptions) << 8);
 373 #  else /* musl libc compatible FE_* values */
 374   fpc = orig_fpc ^ ((orig_fpc ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 375   if ((fpc & 0x00000300) == 0)
 376     /* Clear the corresponding bits of the "data exception code".  */
 377     fpc &= ~((FE_ALL_EXCEPT & exceptions) >> 8);
 378 #  endif
 379   if (fpc != orig_fpc)
 380     _FPU_SETCW (fpc);
 381   /* Possibly some new exception flags have been set.  But just storing them
 382      does not cause a trap to be executed (when traps are enabled).  */
 383   return 0;
 384 }
 385
 386 # elif defined __sh__
 387
 388 /* On glibc, fexcept_t is binary-equivalent to an 'unsigned short'.
 389    On all other OSes, fexcept_t is binary-equivalent to an 'unsigned int'.
 390    A simple C cast does the necessary conversion.  */
 391
 392 int
 393 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 394 {
 395   unsigned int desired_flags = (unsigned int) *saved_flags;
 396   unsigned int fpscr, orig_fpscr;
 397   _FPU_GETCW (orig_fpscr);
 398   fpscr = orig_fpscr ^ ((orig_fpscr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 399   if (fpscr != orig_fpscr)
 400     _FPU_SETCW (fpscr);
 401   /* Possibly some new exception flags have been set.  But just storing them
 402      does not cause a trap to be executed (when traps are enabled).  */
 403   return 0;
 404 }
 405
 406 # elif defined __sparc
 407
 408 /* On all OSes except Solaris, fexcept_t is binary-equivalent to an 'unsigned long'.
 409    On Solaris, fexcept_t is an 'int'.
 410    A simple C cast does the necessary conversion.  */
 411
 412 int
 413 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 414 {
 415   unsigned long desired_flags = (unsigned long) *saved_flags;
 416   unsigned long fsr, orig_fsr;
 417   _FPU_GETCW (orig_fsr);
 418 #  if FE_INEXACT == 32 /* glibc compatible FE_* values */
 419   fsr = orig_fsr ^ ((orig_fsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 420 #  else /* Solaris compatible FE_* values */
 421   fsr = orig_fsr ^ ((orig_fsr ^ (desired_flags << 5)) & ((FE_ALL_EXCEPT & exceptions) << 5));
 422 #  endif
 423   if (fsr != orig_fsr)
 424     _FPU_SETCW (fsr);
 425   /* Possibly some new exception flags have been set.  But just storing them
 426      does not cause a trap to be executed (when traps are enabled).  */
 427   return 0;
 428 }
 429
 430 # else
 431
 432 #  if defined __GNUC__ || defined __clang__
 433 #   warning "Unknown CPU / architecture. Please report your platform and compiler to <bug-gnulib@gnu.org>."
 434 #  endif
 435 #  define NEED_FALLBACK 1
 436
 437 # endif
 438
 439 #else
 440
 441 /* The compiler does not support __asm__ statements or equivalent
 442    intrinsics.  */
 443
 444 # if (defined __sun || __GLIBC__ >= 2) && ((defined __x86_64__ || defined _M_X64) || (defined __i386 || defined _M_IX86)) && defined __SUNPRO_C
 445 /* Solaris/i386, Solaris/x86_64, glibc/i386, glibc/x86_64, with SunPRO C.  */
 446
 447 /* On these Solaris platforms, fpsetsticky cannot be used here, because it may
 448    generate traps (since fpsetsticky calls _putsw, which modifies the control
 449    word of the 387 unit).  Instead, we need to modify only the flags in the SSE
 450    unit.  */
 451
 452 /* Accessors for the mxcsr register.  Fortunately, the SunPRO C compiler
 453    supports a poor form of 'asm'.  */
 454
 455 static void
 456 getssecw (unsigned int *mxcsr_p)
 457 {
 458 #  if defined __x86_64__ || defined _M_X64
 459   asm ("stmxcsr (%rdi)");
 460 #  else
 461   /* The compiler generates a stack frame.  Therefore the first argument is in
 462      8(%ebp), not in 4(%esp).  */
 463   asm ("movl 8(%ebp),%eax");
 464   asm ("stmxcsr (%eax)");
 465 #  endif
 466 }
 467
 468 static void
 469 setssecw (unsigned int const *mxcsr_p)
 470 {
 471 #  if defined __x86_64__ || defined _M_X64
 472   asm ("ldmxcsr (%rdi)");
 473 #  else
 474   /* The compiler generates a stack frame.  Therefore the first argument is in
 475      8(%ebp), not in 4(%esp).  */
 476   asm ("movl 8(%ebp),%eax");
 477   asm ("ldmxcsr (%eax)");
 478 #  endif
 479 }
 480
 481 #  if __GLIBC__ >= 2
 482 /* Clears flags in the 387 unit.  */
 483 static void
 484 mask387cw (unsigned short mask)
 485 {
 486 #   if defined __x86_64__ || defined _M_X64
 487   asm ("fnstenv -32(%rsp)");
 488   asm ("andw %di,-28(%rsp)");
 489   asm ("fldenv -32(%rsp)");
 490 #   else
 491   /* The compiler generates a stack frame.  Therefore the first argument is in
 492      8(%ebp), not in 4(%esp).  */
 493   asm ("movl 8(%ebp),%eax");
 494   asm ("fnstenv -32(%esp)");
 495   asm ("andw %ax,-28(%esp)");
 496   asm ("fldenv -32(%esp)");
 497 #   endif
 498 }
 499 #  endif
 500
 501 int
 502 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 503 {
 504   exceptions &= FE_ALL_EXCEPT;
 505   unsigned int desired_flags = (unsigned int) *saved_flags;
 506
 507   /* Modify the flags in the SSE unit.  */
 508   unsigned int mxcsr, orig_mxcsr;
 509   getssecw (&orig_mxcsr);
 510   mxcsr = orig_mxcsr ^ ((orig_mxcsr ^ desired_flags) & exceptions);
 511   if (mxcsr != orig_mxcsr)
 512     setssecw (&mxcsr);
 513
 514 #  if __GLIBC__ >= 2
 515   /* Modify the flags in the 387 unit, but only by clearing bits, not by
 516      setting bits.  */
 517   mask387cw (~ (exceptions & ~desired_flags));
 518 #  endif
 519
 520   return 0;
 521 }
 522
 523 # elif HAVE_FPSETSTICKY
 524 /* FreeBSD ≥ 3.1, NetBSD ≥ 1.1, OpenBSD, IRIX, Solaris, Minix ≥ 3.2.  */
 525
 526 /* Get fpgetsticky, fpsetsticky.  */
 527 #  include <ieeefp.h>
 528 /* The type is called 'fp_except_t' on FreeBSD, but 'fp_except' on
 529    all other systems.  */
 530 #  if !defined __FreeBSD__
 531 #   define fp_except_t fp_except
 532 #  endif
 533
 534 int
 535 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 536 {
 537   unsigned long desired_flags = (unsigned long) *saved_flags;
 538   fp_except_t flags, orig_flags;
 539   orig_flags = fpgetsticky ();
 540   flags = orig_flags ^ ((orig_fsr ^ desired_flags) & FE_ALL_EXCEPT & exceptions);
 541   if (flags != orig_flags)
 542     fpsetsticky (flags);
 543   /* Possibly some new exception flags have been set.  But just storing them
 544      does not cause a trap to be executed (when traps are enabled).  */
 545   return 0;
 546 }
 547
 548 # elif defined _AIX && defined __powerpc__ /* AIX */
 549
 550 #  include <float.h>
 551 #  include <fpxcp.h>
 552
 553 #  include <fptrap.h>
 554
 555 /* Documentation:
 556    <https://www.ibm.com/docs/en/aix/7.3?topic=f-fp-clr-flag-fp-set-flag-fp-read-flag-fp-swap-flag-subroutine>  */
 557
 558 int
 559 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 560 {
 561   exceptions &= FE_ALL_EXCEPT;
 562
 563   unsigned int desired_flags = (unsigned int) *saved_flags;
 564   int exceptions_to_clear = exceptions & ~desired_flags;
 565   int exceptions_to_set = exceptions & desired_flags;
 566
 567   fpflag_t orig_flags = fp_read_flag ();
 568   /* In addition to clearing FE_INVALID (= bit 29), we also need to clear the
 569      individual bits.  */
 570   fpflag_t f_to_clear =
 571     exceptions_to_fpflag (exceptions_to_clear)
 572     | (exceptions_to_clear & FE_INVALID ? 0x01F80700U : 0);
 573   /* Instead of setting FE_INVALID (= bit 29), we need to set one of the
 574      individual bits: bit 10 or, if that does not work, bit 24.  */
 575   fpflag_t f_to_set =
 576     (exceptions_to_set & FE_INVALID
 577      ? exceptions_to_fpflag (exceptions_to_set & ~FE_INVALID) | (1U << 10)
 578      : exceptions_to_fpflag (exceptions_to_set));
 579   if (f_to_clear != 0)
 580     fp_clr_flag (f_to_clear);
 581   if (f_to_set != 0)
 582     {
 583       if ((fegetexcept_impl () & exceptions) != 0)
 584         {
 585           /* Setting the exception flags may trigger a trap.
 586              ISO C 23 § 7.6.4.5 does not allow it.  */
 587           return -1;
 588         }
 589       fp_set_flag (f_to_set);
 590       if (exceptions & FE_INVALID)
 591         {
 592           /* Did it work?  */
 593           if ((fp_read_flag () & FP_INVALID) == 0)
 594             fp_set_flag (1U << 24);
 595         }
 596     }
 597
 598   return 0;
 599 }
 600
 601 # else
 602
 603 #  define NEED_FALLBACK 1
 604
 605 # endif
 606
 607 #endif
 608
 609 #if NEED_FALLBACK
 610
 611 /* A dummy fallback.  */
 612
 613 int
 614 fesetexceptflag (fexcept_t const *saved_flags, int exceptions)
 615 {
 616   if (exceptions != 0)
 617     return -1;
 618   return 0;
 619 }
 620
 621 #endif