| 0,0 → 1,85 |
|---|
| /* @(#)s_log2.c 5.1 93/09/24 */ |
| /* Modification from s_exp10.c Yaakov Selkowitz 2009. */ |
| |
| /* |
| * ==================================================== |
| * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| * |
| * Developed at SunPro, a Sun Microsystems, Inc. business. |
| * Permission to use, copy, modify, and distribute this |
| * software is freely granted, provided that this notice |
| * is preserved. |
| * ==================================================== |
| */ |
| |
| /* |
| FUNCTION |
| <<log2>>, <<log2f>>--base 2 logarithm |
| INDEX |
| log2 |
| INDEX |
| log2f |
| |
| ANSI_SYNOPSIS |
| #include <math.h> |
| double log2(double <[x]>); |
| float log2f(float <[x]>); |
| |
| DESCRIPTION |
| The <<log2>> functions compute the base-2 logarithm of <[x]>. A domain error |
| occurs if the argument is less than zero. A range error occurs if the |
| argument is zero. |
| |
| The Newlib implementations are not full, intrinisic calculations, but |
| rather are derivatives based on <<log>>. (Accuracy might be slightly off from |
| a direct calculation.) In addition to functions, they are also implemented as |
| macros defined in math.h: |
| . #define log2(x) (log (x) / _M_LN2) |
| . #define log2f(x) (logf (x) / (float) _M_LN2) |
| To use the functions instead, just undefine the macros first. |
| |
| You can use the (non-ANSI) function <<matherr>> to specify error |
| handling for these functions, indirectly through the respective <<log>> |
| function. |
| |
| RETURNS |
| The <<log2>> functions return |
| @ifnottex |
| <<log base-2(<[x]>)>> |
| @end ifnottex |
| @tex |
| $log_2(x)$ |
| @end tex |
| on success. |
| When <[x]> is zero, the |
| returned value is <<-HUGE_VAL>> and <<errno>> is set to <<ERANGE>>. |
| When <[x]> is negative, the returned value is NaN (not a number) and |
| <<errno>> is set to <<EDOM>>. You can control the error behavior via |
| <<matherr>>. |
| |
| PORTABILITY |
| C99, POSIX, System V Interface Definition (Issue 6). |
| */ |
| |
| /* |
| * wrapper log2(x) |
| */ |
| |
| #include "fdlibm.h" |
| #include <errno.h> |
| #include <math.h> |
| #undef log2 |
| |
| #ifndef _DOUBLE_IS_32BITS |
| |
| #ifdef __STDC__ |
| double log2(double x) /* wrapper log2 */ |
| #else |
| double log2(x) /* wrapper log2 */ |
| double x; |
| #endif |
| { |
| return (log(x) / M_LN2); |
| } |
| |
| #endif /* defined(_DOUBLE_IS_32BITS) */ |