Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 1 | /*===-- floatdisf.c - Implement __floatdisf -------------------------------=== |
| 2 | * |
| 3 | * The LLVM Compiler Infrastructure |
| 4 | * |
| 5 | * This file is distributed under the University of Illinois Open Source |
| 6 | * License. See LICENSE.TXT for details. |
| 7 | * |
| 8 | *===----------------------------------------------------------------------=== |
| 9 | * |
| 10 | * This file implements __floatdisf for the compiler_rt library. |
| 11 | * |
| 12 | *===----------------------------------------------------------------------=== |
| 13 | */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 14 | |
| 15 | #include "int_lib.h" |
| 16 | #include <float.h> |
| 17 | |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 18 | /* Returns: convert a to a float, rounding toward even.*/ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 19 | |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 20 | /* Assumption: float is a IEEE 32 bit floating point type |
| 21 | * di_int is a 64 bit integral type |
| 22 | */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 23 | |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 24 | /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 25 | |
| 26 | float |
| 27 | __floatdisf(di_int a) |
| 28 | { |
| 29 | if (a == 0) |
| 30 | return 0.0F; |
| 31 | const unsigned N = sizeof(di_int) * CHAR_BIT; |
| 32 | const di_int s = a >> (N-1); |
| 33 | a = (a ^ s) - s; |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 34 | int sd = N - __builtin_clzll(a); /* number of significant digits */ |
| 35 | int e = sd - 1; /* exponent */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 36 | if (sd > FLT_MANT_DIG) |
| 37 | { |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 38 | /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx |
| 39 | * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR |
| 40 | * 12345678901234567890123456 |
| 41 | * 1 = msb 1 bit |
| 42 | * P = bit FLT_MANT_DIG-1 bits to the right of 1 |
| 43 | * Q = bit FLT_MANT_DIG bits to the right of 1 |
| 44 | * R = "or" of all bits to the right of Q |
| 45 | */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 46 | switch (sd) |
| 47 | { |
| 48 | case FLT_MANT_DIG + 1: |
| 49 | a <<= 1; |
| 50 | break; |
| 51 | case FLT_MANT_DIG + 2: |
| 52 | break; |
| 53 | default: |
| 54 | a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) | |
| 55 | ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0); |
| 56 | }; |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 57 | /* finish: */ |
| 58 | a |= (a & 4) != 0; /* Or P into R */ |
| 59 | ++a; /* round - this step may add a significant bit */ |
| 60 | a >>= 2; /* dump Q and R */ |
| 61 | /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 62 | if (a & ((du_int)1 << FLT_MANT_DIG)) |
| 63 | { |
| 64 | a >>= 1; |
| 65 | ++e; |
| 66 | } |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 67 | /* a is now rounded to FLT_MANT_DIG bits */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 68 | } |
| 69 | else |
| 70 | { |
| 71 | a <<= (FLT_MANT_DIG - sd); |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 72 | /* a is now rounded to FLT_MANT_DIG bits */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 73 | } |
| 74 | float_bits fb; |
Edward O'Callaghan | 37a6a45 | 2009-08-07 20:30:09 +0000 | [diff] [blame^] | 75 | fb.u = ((su_int)s & 0x80000000) | /* sign */ |
| 76 | ((e + 127) << 23) | /* exponent */ |
| 77 | ((su_int)a & 0x007FFFFF); /* mantissa */ |
Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame] | 78 | return fb.f; |
| 79 | } |