newlib/libm/math/w_log10.c

   1
   2 /* @(#)w_log10.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15 FUNCTION
  16         <<log10>>, <<log10f>>---base 10 logarithms
  17
  18 INDEX
  19 log10
  20 INDEX
  21 log10f
  22
  23 SYNOPSIS
  24         #include <math.h>
  25         double log10(double <[x]>);
  26         float log10f(float <[x]>);
  27
  28 DESCRIPTION
  29 <<log10>> returns the base 10 logarithm of <[x]>.
  30 It is implemented as <<log(<[x]>) / log(10)>>.
  31
  32 <<log10f>> is identical, save that it takes and returns <<float>> values.
  33
  34 RETURNS
  35 <<log10>> and <<log10f>> return the calculated value.
  36
  37 See the description of <<log>> for information on errors.
  38
  39 PORTABILITY
  40 <<log10>> is ANSI C.  <<log10f>> is an extension.
  41
  42  */
  43
  44 /*
  45  * wrapper log10(X)
  46  */
  47
  48 #include "fdlibm.h"
  49 #include <errno.h>
  50
  51 #ifndef _DOUBLE_IS_32BITS
  52
  53 #ifdef __STDC__
  54         double log10(double x)          /* wrapper log10 */
  55 #else
  56         double log10(x)                 /* wrapper log10 */
  57         double x;
  58 #endif
  59 {
  60 #ifdef _IEEE_LIBM
  61         return __ieee754_log10(x);
  62 #else
  63         double z;
  64         z = __ieee754_log10(x);
  65         if(_LIB_VERSION == _IEEE_ || isnan(x)) return z;
  66         if(x<=0.0) {
  67             if(x==0.0) {
  68                 /* log10(0) */
  69                 errno = ERANGE;
  70                 return -HUGE_VAL;
  71             } else {
  72                 /* log10(x<0) */
  73                 errno = EDOM;
  74                 return nan("");
  75             }
  76         } else
  77             return z;
  78 #endif
  79 }
  80
  81 #endif /* defined(_DOUBLE_IS_32BITS) */