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Diffstat (limited to 'compiler-rt/lib/builtins/floatuntitf.c')
-rw-r--r-- | compiler-rt/lib/builtins/floatuntitf.c | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/compiler-rt/lib/builtins/floatuntitf.c b/compiler-rt/lib/builtins/floatuntitf.c new file mode 100644 index 000000000000..d308d3118d03 --- /dev/null +++ b/compiler-rt/lib/builtins/floatuntitf.c @@ -0,0 +1,75 @@ +//===-- lib/floatuntitf.c - uint128 -> 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 tu_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 tu_int to a fp_t, rounding toward even. + +// Assumption: fp_t is a IEEE 128 bit floating point type +// tu_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 __floatuntitf(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 > 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 = (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 = (du_int)(e + 16383) << 48 // exponent + | ((a >> 64) & 0x0000ffffffffffffLL); // significand + fb.u.low.all = (du_int)(a); + return fb.f; +} + +#endif |