80 lines
2.8 KiB
C
80 lines
2.8 KiB
C
//===-- lib/floatuntitf.c - uint128 -> quad-precision conversion --*- C -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements tu_int to quad-precision conversion for the
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// compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
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// mode.
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//
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//===----------------------------------------------------------------------===//
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#define QUAD_PRECISION
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#include "fp_lib.h"
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#include "int_lib.h"
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/* Returns: convert a tu_int to a fp_t, rounding toward even. */
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/* Assumption: fp_t is a IEEE 128 bit floating point type
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* tu_int is a 128 bit integral type
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*/
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/* seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm |
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* mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
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*/
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#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
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COMPILER_RT_ABI fp_t
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__floatuntitf(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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*/
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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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long_double_bits fb;
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fb.u.high.all = (du_int)(e + 16383) << 48 /* exponent */
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| ((a >> 64) & 0x0000ffffffffffffLL); /* significand */
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fb.u.low.all = (du_int)(a);
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return fb.f;
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}
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#endif
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