floatuntidf.c
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//===-- floatuntidf.c - Implement __floatuntidf ---------------------------===//
//
// 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 __floatuntidf for the compiler_rt library.
//
//===----------------------------------------------------------------------===//
#include "int_lib.h"
#ifdef CRT_HAS_128BIT
// Returns: convert a to a double, rounding toward even.
// Assumption: double is a IEEE 64 bit floating point type
// tu_int is a 128 bit integral type
// seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
// mmmm
COMPILER_RT_ABI double __floatuntidf(tu_int a) {
if (a == 0)
return 0.0;
const unsigned N = sizeof(tu_int) * CHAR_BIT;
int sd = N - __clzti2(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 = (a >> (sd - (DBL_MANT_DIG + 2))) |
((a & ((tu_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 & ((tu_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 = ((e + 1023) << 20) | // exponent
((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
fb.u.s.low = (su_int)a; // mantissa-low
return fb.f;
}
#endif // CRT_HAS_128BIT