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1
2/*
3 * logb.c
4 *
5 * by Ian Ollmann
6 *
7 * Copyright (c) 2007, Apple Inc. All Rights Reserved.
8 *
9 * Unix 2003 implementation of logb()
10 */
11
12#include <math.h>
13#include <stdint.h>
14
15#ifdef ARMLIBM_SET_FLAGS
16
17#include "required_arithmetic.h"
18
19float logbf( float x )
20{
21 union{ float f; uint32_t u;}u = {x};
22
23 u.u &= 0x7fffffffU;
24 int32_t exp = u.u >> 23;
25
26 if( __builtin_expect( (uint32_t) exp - 1U >= 254, 0 ) )
27 { // +-0, +-denorm, +-inf, NaN
28 if( 0.0f == x )
29 return required_divide_float( -1.0f, 0.0f ); //set div/0, return -inf
30
31 if( x != x )
32 return x + x;
33
34 if( u.u == 0x7f800000U )
35 return __builtin_inff();
36
37 u.u |= 0x3f800000U;
38 u.f -= 1.0f;
39 exp = u.u >> 23;
40
41 return (float) (exp - (127+126));
42 }
43
44 return (float) (exp - 127);
45}
46
47#else
48
49float logbf( float x )
50{
51 union{ float f; uint32_t u;}u = {x};
52
53 u.u &= 0x7fffffffU;
54 int32_t exp = u.u >> 23;
55
56 if( __builtin_expect( (uint32_t) exp - 1U >= 254, 0 ) )
57 { // +-0, +-denorm, +-inf, NaN
58 if( 0.0f == x )
59 return -__builtin_inff(); //set div/0, return -inf
60
61 if( x != x )
62 return x + x;
63
64 if( u.u == 0x7f800000U )
65 return __builtin_inff();
66
67 u.u |= 0x3f800000U;
68 u.f -= 1.0f;
69 exp = u.u >> 23;
70
71 return (float) (exp - (127+126));
72 }
73
74 return (float) (exp - 127);
75}
76
77#endif