diff options
Diffstat (limited to 'newlib/libm/common/s_log2.c')
| -rw-r--r-- | newlib/libm/common/s_log2.c | 46 |
1 files changed, 29 insertions, 17 deletions
diff --git a/newlib/libm/common/s_log2.c b/newlib/libm/common/s_log2.c index 4683960eb..7ad2cd88b 100644 --- a/newlib/libm/common/s_log2.c +++ b/newlib/libm/common/s_log2.c @@ -14,7 +14,7 @@ /* FUNCTION - <<log2>>, <<log2f>>---base 2 logarithm + <<log2>>, <<log2f>>--base 2 logarithm INDEX log2 INDEX @@ -25,28 +25,40 @@ ANSI_SYNOPSIS double log2(double <[x]>); float log2f(float <[x]>); -TRAD_SYNOPSIS - #include <math.h> - double log2(<[x]>); - double <[x]>; - - float log2f(<[x]>); - float <[x]>; - DESCRIPTION - <<log2>> returns the base 2 logarithm of <[x]>. +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_LOG2_E) +. #define log2f(x) (logf (x) / (float) _M_LOG2_E) +To use the functions instead, just undefine the macros first. - <<log2f>> is identical, save that it takes and returns <<float>> values. +You can use the (non-ANSI) function <<matherr>> to specify error +handling for these functions, indirectly through the respective <<log>> +function. RETURNS - On success, <<log2>> and <<log2f>> return the calculated value. - If the result underflows, the returned value is <<0>>. If the - result overflows, the returned value is <<HUGE_VAL>>. In - either case, <<errno>> is set to <<ERANGE>>. +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 - <<log2>> and <<log2f>> are required by ISO/IEC 9899:1999 and the - System V Interface Definition (Issue 6). +C99, POSIX, System V Interface Definition (Issue 6). */ /* |