05a4212cc7
Use of long double can be error-prone since it could be one of 80-bit extended precision float, IEEE 128-bit float, or IBM 128-bit float. Instead use an explicit xf_float typedef for the remaining cases where long double is being used in the implementation. This patch does not touch the PPC specializations which still use long double.
71 lines
2.4 KiB
C
71 lines
2.4 KiB
C
//===-- floatuntixf.c - Implement __floatuntixf ---------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements __floatuntixf for the compiler_rt library.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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#ifdef CRT_HAS_128BIT
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// Returns: convert a to a long double, rounding toward even.
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// Assumption: long double is a IEEE 80 bit floating point type padded to 128
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// bits tu_int is a 128 bit integral type
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// gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee
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// eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
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// mmmm mmmm mmmm
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COMPILER_RT_ABI xf_float __floatuntixf(tu_int a) {
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if (a == 0)
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return 0.0;
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const unsigned N = sizeof(tu_int) * CHAR_BIT;
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int sd = N - __clzti2(a); // number of significant digits
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int e = sd - 1; // exponent
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if (sd > LDBL_MANT_DIG) {
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// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
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// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
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// 12345678901234567890123456
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// 1 = msb 1 bit
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// P = bit LDBL_MANT_DIG-1 bits to the right of 1
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// Q = bit LDBL_MANT_DIG bits to the right of 1
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// R = "or" of all bits to the right of Q
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switch (sd) {
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case LDBL_MANT_DIG + 1:
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a <<= 1;
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break;
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case LDBL_MANT_DIG + 2:
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break;
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default:
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a = (a >> (sd - (LDBL_MANT_DIG + 2))) |
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((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0);
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};
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// finish:
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a |= (a & 4) != 0; // Or P into R
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++a; // round - this step may add a significant bit
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a >>= 2; // dump Q and R
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// a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
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if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
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a >>= 1;
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++e;
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}
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// a is now rounded to LDBL_MANT_DIG bits
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} else {
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a <<= (LDBL_MANT_DIG - sd);
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// a is now rounded to LDBL_MANT_DIG bits
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}
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xf_bits fb;
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fb.u.high.s.low = (e + 16383); // exponent
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fb.u.low.all = (du_int)a; // mantissa
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return fb.f;
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}
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#endif
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