zircon/third_party/ulib/musl/src/fenv/x86_64/fenv.c

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <fenv.h>
#include <stdint.h>
#include <x86intrin.h>
#include <zircon/compiler.h>

#define ROUND_MASK (FE_DOWNWARD | FE_UPWARD | FE_TOWARDZERO)
_Static_assert((ROUND_MASK << 3) == _MM_ROUND_MASK, "");

static inline uint16_t get_x87_sw(void) {
  uint16_t sw;
  __asm__("fnstsw %0" : "=a"(sw));
  return sw;
}

static inline uint16_t get_x87_cw(void) {
  uint16_t cw;
  __asm__("fnstcw %0" : "=m"(cw));
  return cw;
}

static inline void set_x87_cw(uint16_t cw) { __asm__("fldcw %0" ::"m"(cw)); }

int fegetround(void) { return _MM_GET_ROUNDING_MODE() >> 3; }

__LOCAL int __fesetround(int round) {
  set_x87_cw((get_x87_cw() & ~ROUND_MASK) | round);
  _MM_SET_ROUNDING_MODE(round << 3);
  return 0;
}

int feclearexcept(int mask) {
  uint16_t sw = get_x87_sw();
  if (sw & mask & FE_ALL_EXCEPT)
    __asm__("fnclex");
  uint32_t mxcsr = _mm_getcsr();
  mxcsr |= sw & FE_ALL_EXCEPT;
  if (mxcsr & mask & FE_ALL_EXCEPT)
    _mm_setcsr(mxcsr & ~(mask & FE_ALL_EXCEPT));
  return 0;
}

int feraiseexcept(int mask) {
  _mm_setcsr(_mm_getcsr() | (mask & FE_ALL_EXCEPT));
  return 0;
}

int fetestexcept(int mask) { return (_mm_getcsr() | get_x87_sw()) & mask & FE_ALL_EXCEPT; }

int fegetenv(fenv_t* env) {
  __asm__(
      "fnstenv %0\n"
      "stmxcsr %1"
      : "=m"(*env), "=m"(env->__mxcsr));
  return 0;
}

static inline void install_fenv(const fenv_t* env) {
  __asm__(
      "fldenv %0\n"
      "ldmxcsr %1" ::"m"(*env),
      "m"(env->__mxcsr));
}

int fesetenv(const fenv_t* env) {
  install_fenv(likely(env != FE_DFL_ENV) ? env
                                         : &(fenv_t){
                                               .__control_word = 0x37f,
                                               .__tags = 0xffff,
                                               .__mxcsr = 0x1f80,
                                           });
  return 0;
}