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/* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------=== |
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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 __floatuntidf for the compiler_rt library. |
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* |
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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 double, rounding toward even. */ |
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/* Assumption: double is a IEEE 64 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 mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ |
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COMPILER_RT_ABI double |
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__floatuntidf(tu_int a) |
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{ |
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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 > DBL_MANT_DIG) |
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{ |
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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 DBL_MANT_DIG-1 bits to the right of 1 |
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* Q = bit DBL_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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{ |
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case DBL_MANT_DIG + 1: |
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a <<= 1; |
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break; |
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case DBL_MANT_DIG + 2: |
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break; |
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default: |
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a = (a >> (sd - (DBL_MANT_DIG+2))) | |
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((a & ((tu_int)(-1) >> ((N + DBL_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 DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ |
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if (a & ((tu_int)1 << DBL_MANT_DIG)) |
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{ |
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a >>= 1; |
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++e; |
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} |
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/* a is now rounded to DBL_MANT_DIG bits */ |
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} |
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else |
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{ |
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a <<= (DBL_MANT_DIG - sd); |
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/* a is now rounded to DBL_MANT_DIG bits */ |
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} |
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double_bits fb; |
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fb.u.s.high = ((e + 1023) << 20) | /* exponent */ |
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((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ |
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fb.u.s.low = (su_int)a; /* mantissa-low */ |
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return fb.f; |
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} |
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#endif /* CRT_HAS_128BIT */ |