floattitf.c
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//===-- lib/floattitf.c - int128 -> quad-precision conversion -----*- C -*-===//
//
// 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 ti_int to quad-precision conversion for the
// compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
// mode.
//
//===----------------------------------------------------------------------===//
#define QUAD_PRECISION
#include "fp_lib.h"
#include "int_lib.h"
// Returns: convert a ti_int to a fp_t, rounding toward even.
// Assumption: fp_t is a IEEE 128 bit floating point type
// ti_int is a 128 bit integral type
// seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
// mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
// mmmm mmmm mmmm
#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
COMPILER_RT_ABI fp_t __floattitf(ti_int a) {
if (a == 0)
return 0.0;
const unsigned N = sizeof(ti_int) * CHAR_BIT;
const ti_int s = a >> (N - 1);
a = (a ^ s) - s;
int sd = N - __clzti2(a); // number of significant digits
int e = sd - 1; // exponent
if (sd > LDBL_MANT_DIG) {
// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
// 12345678901234567890123456
// 1 = msb 1 bit
// P = bit LDBL_MANT_DIG-1 bits to the right of 1
// Q = bit LDBL_MANT_DIG bits to the right of 1
// R = "or" of all bits to the right of Q
switch (sd) {
case LDBL_MANT_DIG + 1:
a <<= 1;
break;
case LDBL_MANT_DIG + 2:
break;
default:
a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) |
((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
a >>= 1;
++e;
}
// a is now rounded to LDBL_MANT_DIG bits
} else {
a <<= (LDBL_MANT_DIG - sd);
// a is now rounded to LDBL_MANT_DIG bits
}
long_double_bits fb;
fb.u.high.all = (s & 0x8000000000000000LL) // sign
| (du_int)(e + 16383) << 48 // exponent
| ((a >> 64) & 0x0000ffffffffffffLL); // significand
fb.u.low.all = (du_int)(a);
return fb.f;
}
#endif