diff options
Diffstat (limited to 'uceil_log2.c')
| -rw-r--r-- | uceil_log2.c | 27 |
1 files changed, 26 insertions, 1 deletions
diff --git a/uceil_log2.c b/uceil_log2.c index f7ba603cd..ab3bcd8ab 100644 --- a/uceil_log2.c +++ b/uceil_log2.c @@ -24,11 +24,14 @@ MA 02111-1307, USA. */ #include "mpfr.h" #include "mpfr-impl.h" -/* returns ceil(log(d)/log(2)) */ +/* returns ceil(log(d)/log(2)) if d > 0, + -1023 if d = +0, + and floor(log(-d)/log(2))+1 if d < 0*/ long __gmpfr_ceil_log2 (double d) { long exp; +#if _GMP_IEEE_FLOATS union ieee_double_extract x; x.d = d; @@ -37,4 +40,26 @@ __gmpfr_ceil_log2 (double d) if (x.d != 1.0) /* d: not a power of two? */ exp++; return exp; +#else + double m; + + if (d < 0.0) + return __gmpfr_floor_log2(-d)+1; + else if (d == 0.0) + return -1023; + else if (d >= 1.0) + { + exp = 0; + for( m= 1.0 ; m < d ; m *=2.0 ) + exp++; + } + else + { + exp = 1; + for( m= 1.0 ; m >= d ; m *= (1.0/2.0) ) + exp--; + } +#endif + return exp; } + |