floatdidf.c
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//===-- floatdidf.c - Implement __floatdidf -------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements __floatdidf for the compiler_rt library.
//
//===----------------------------------------------------------------------===//
#include "int_lib.h"
// Returns: convert a to a double, rounding toward even.
// Assumption: double is a IEEE 64 bit floating point type
// di_int is a 64 bit integral type
// seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
// mmmm
#ifndef __SOFT_FP__
// Support for systems that have hardware floating-point; we'll set the inexact
// flag as a side-effect of this computation.
COMPILER_RT_ABI double __floatdidf(di_int a) {
static const double twop52 = 4503599627370496.0; // 0x1.0p52
static const double twop32 = 4294967296.0; // 0x1.0p32
union {
int64_t x;
double d;
} low = {.d = twop52};
const double high = (int32_t)(a >> 32) * twop32;
low.x |= a & INT64_C(0x00000000ffffffff);
const double result = (high - twop52) + low.d;
return result;
}
#else
// Support for systems that don't have hardware floating-point; there are no
// flags to set, and we don't want to code-gen to an unknown soft-float
// implementation.
COMPILER_RT_ABI double __floatdidf(di_int a) {
if (a == 0)
return 0.0;
const unsigned N = sizeof(di_int) * CHAR_BIT;
const di_int s = a >> (N - 1);
a = (a ^ s) - s;
int sd = N - __builtin_clzll(a); // number of significant digits
int e = sd - 1; // exponent
if (sd > DBL_MANT_DIG) {
// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
// 12345678901234567890123456
// 1 = msb 1 bit
// P = bit DBL_MANT_DIG-1 bits to the right of 1
// Q = bit DBL_MANT_DIG bits to the right of 1
// R = "or" of all bits to the right of Q
switch (sd) {
case DBL_MANT_DIG + 1:
a <<= 1;
break;
case DBL_MANT_DIG + 2:
break;
default:
a = ((du_int)a >> (sd - (DBL_MANT_DIG + 2))) |
((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0);
};
// finish:
a |= (a & 4) != 0; // Or P into R
++a; // round - this step may add a significant bit
a >>= 2; // dump Q and R
// a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits
if (a & ((du_int)1 << DBL_MANT_DIG)) {
a >>= 1;
++e;
}
// a is now rounded to DBL_MANT_DIG bits
} else {
a <<= (DBL_MANT_DIG - sd);
// a is now rounded to DBL_MANT_DIG bits
}
double_bits fb;
fb.u.s.high = ((su_int)s & 0x80000000) | // sign
((su_int)(e + 1023) << 20) | // exponent
((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
fb.u.s.low = (su_int)a; // mantissa-low
return fb.f;
}
#endif
#if defined(__ARM_EABI__)
#if defined(COMPILER_RT_ARMHF_TARGET)
AEABI_RTABI double __aeabi_l2d(di_int a) { return __floatdidf(a); }
#else
COMPILER_RT_ALIAS(__floatdidf, __aeabi_l2d)
#endif
#endif