Stephen Hines | 2d1fdb2 | 2014-05-28 23:58:16 -0700 | [diff] [blame^] | 1 | /* ===-- floattidf.c - Implement __floattidf -------------------------------=== |
| 2 | * |
| 3 | * The LLVM Compiler Infrastructure |
| 4 | * |
| 5 | * This file is dual licensed under the MIT and the University of Illinois Open |
| 6 | * Source Licenses. See LICENSE.TXT for details. |
| 7 | * |
| 8 | * ===----------------------------------------------------------------------=== |
| 9 | * |
| 10 | * This file implements __floattidf for the compiler_rt library. |
| 11 | * |
| 12 | * ===----------------------------------------------------------------------=== |
| 13 | */ |
| 14 | |
| 15 | #include "int_lib.h" |
| 16 | |
| 17 | #ifdef CRT_HAS_128BIT |
| 18 | |
| 19 | /* Returns: convert a to a double, rounding toward even.*/ |
| 20 | |
| 21 | /* Assumption: double is a IEEE 64 bit floating point type |
| 22 | * ti_int is a 128 bit integral type |
| 23 | */ |
| 24 | |
| 25 | /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ |
| 26 | |
| 27 | COMPILER_RT_ABI double |
| 28 | __floattidf(ti_int a) |
| 29 | { |
| 30 | if (a == 0) |
| 31 | return 0.0; |
| 32 | const unsigned N = sizeof(ti_int) * CHAR_BIT; |
| 33 | const ti_int s = a >> (N-1); |
| 34 | a = (a ^ s) - s; |
| 35 | int sd = N - __clzti2(a); /* number of significant digits */ |
| 36 | int e = sd - 1; /* exponent */ |
| 37 | if (sd > DBL_MANT_DIG) |
| 38 | { |
| 39 | /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx |
| 40 | * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR |
| 41 | * 12345678901234567890123456 |
| 42 | * 1 = msb 1 bit |
| 43 | * P = bit DBL_MANT_DIG-1 bits to the right of 1 |
| 44 | * Q = bit DBL_MANT_DIG bits to the right of 1 |
| 45 | * R = "or" of all bits to the right of Q |
| 46 | */ |
| 47 | switch (sd) |
| 48 | { |
| 49 | case DBL_MANT_DIG + 1: |
| 50 | a <<= 1; |
| 51 | break; |
| 52 | case DBL_MANT_DIG + 2: |
| 53 | break; |
| 54 | default: |
| 55 | a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) | |
| 56 | ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); |
| 57 | }; |
| 58 | /* finish: */ |
| 59 | a |= (a & 4) != 0; /* Or P into R */ |
| 60 | ++a; /* round - this step may add a significant bit */ |
| 61 | a >>= 2; /* dump Q and R */ |
| 62 | /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ |
| 63 | if (a & ((tu_int)1 << DBL_MANT_DIG)) |
| 64 | { |
| 65 | a >>= 1; |
| 66 | ++e; |
| 67 | } |
| 68 | /* a is now rounded to DBL_MANT_DIG bits */ |
| 69 | } |
| 70 | else |
| 71 | { |
| 72 | a <<= (DBL_MANT_DIG - sd); |
| 73 | /* a is now rounded to DBL_MANT_DIG bits */ |
| 74 | } |
| 75 | double_bits fb; |
| 76 | fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */ |
| 77 | ((e + 1023) << 20) | /* exponent */ |
| 78 | ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ |
| 79 | fb.u.s.low = (su_int)a; /* mantissa-low */ |
| 80 | return fb.f; |
| 81 | } |
| 82 | |
| 83 | #endif /* CRT_HAS_128BIT */ |