Book a Demo!
CoCalc Logo Icon
StoreFeaturesDocsShareSupportNewsAboutPoliciesSign UpSign In
godotengine
GitHub Repository: godotengine/godot
 Path: blob/master/thirdparty/sdl/libm/e_log10.c
9903 views
1
#include "SDL_internal.h"

2
/*

3
 * ====================================================

4
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

5
 *

6
 * Developed at SunPro, a Sun Microsystems, Inc. business.

7
 * Permission to use, copy, modify, and distribute this

8
 * software is freely granted, provided that this notice

9
 * is preserved.

10
 * ====================================================

11
 */

12


13
#if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */

14
/* C4723: potential divide by zero. */

15
#pragma warning ( disable : 4723 )

16
#endif

17


18
/* __ieee754_log10(x)

19
 * Return the base 10 logarithm of x

20
 *

21
 * Method :

22
 *	Let log10_2hi = leading 40 bits of log10(2) and

23
 *	    log10_2lo = log10(2) - log10_2hi,

24
 *	    ivln10   = 1/log(10) rounded.

25
 *	Then

26
 *		n = ilogb(x),

27
 *		if(n<0)  n = n+1;

28
 *		x = scalbn(x,-n);

29
 *		log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))

30
 *

31
 * Note 1:

32
 *	To guarantee log10(10**n)=n, where 10**n is normal, the rounding

33
 *	mode must set to Round-to-Nearest.

34
 * Note 2:

35
 *	[1/log(10)] rounded to 53 bits has error  .198   ulps;

36
 *	log10 is monotonic at all binary break points.

37
 *

38
 * Special cases:

39
 *	log10(x) is NaN with signal if x < 0;

40
 *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;

41
 *	log10(NaN) is that NaN with no signal;

42
 *	log10(10**N) = N  for N=0,1,...,22.

43
 *

44
 * Constants:

45
 * The hexadecimal values are the intended ones for the following constants.

46
 * The decimal values may be used, provided that the compiler will convert

47
 * from decimal to binary accurately enough to produce the hexadecimal values

48
 * shown.

49
 */

50


51
#include "math_libm.h"

52
#include "math_private.h"

53


54
static const double

55
two54      =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */

56
ivln10     =  4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */

57
log10_2hi  =  3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */

58
log10_2lo  =  3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */

59


60
static const double zero = 0.0;

61


62
double attribute_hidden __ieee754_log10(double x)

63
{

64
	double y,z;

65
	int32_t i,k,hx;

66
	u_int32_t lx;

67


68
	EXTRACT_WORDS(hx,lx,x);

69


70
        k=0;

71
        if (hx < 0x00100000) {                  /* x < 2**-1022  */

72
            if (((hx&0x7fffffff)|lx)==0)

73
                return -two54/zero;             /* log(+-0)=-inf */

74
            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */

75
            k -= 54; x *= two54; /* subnormal number, scale up x */

76
	    GET_HIGH_WORD(hx,x);

77
        }

78
	if (hx >= 0x7ff00000) return x+x;

79
	k += (hx>>20)-1023;

80
	i  = ((u_int32_t)k&0x80000000)>>31;

81
        hx = (hx&0x000fffff)|((0x3ff-i)<<20);

82
        y  = (double)(k+i);

83
	SET_HIGH_WORD(x,hx);

84
	z  = y*log10_2lo + ivln10*__ieee754_log(x);

85
	return  z+y*log10_2hi;

86
}

87


88
/*

89
 * wrapper log10(X)

90
 */

91
#ifndef _IEEE_LIBM

92
double log10(double x)

93
{

94
	double z = __ieee754_log10(x);

95
	if (_LIB_VERSION == _IEEE_ || isnan(x))

96
		return z;

97
	if (x <= 0.0) {

98
		if(x == 0.0)

99
			return __kernel_standard(x, x, 18); /* log10(0) */

100
		return __kernel_standard(x, x, 19); /* log10(x<0) */

101
	}

102
	return z;

103
}

104
#else

105
strong_alias(__ieee754_log10, log10)

106
#endif

107
libm_hidden_def(log10)

108


109