diff options
Diffstat (limited to 'stdlib/erand48_r.c')
| -rw-r--r-- | stdlib/erand48_r.c | 42 |
1 files changed, 26 insertions, 16 deletions
diff --git a/stdlib/erand48_r.c b/stdlib/erand48_r.c index 86d2f734d9..ab41474aca 100644 --- a/stdlib/erand48_r.c +++ b/stdlib/erand48_r.c @@ -17,9 +17,15 @@ License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ -#include <errno.h> -#include <math.h> #include <stdlib.h> +#include "gmp.h" +#include "gmp-mparam.h" +#include <float.h> + + +/* Function to construct a floating point number from an MP integer + containing the fraction bits, a base 2 exponent, and a sign flag. */ +extern double __mpn_construct_double (mp_srcptr mpn, int exponent, int neg); int erand48_r (xsubi, buffer, result) @@ -27,26 +33,30 @@ erand48_r (xsubi, buffer, result) struct drand48_data *buffer; double *result; { - int i; - - /* Be generous for the arguments, detect some errors. */ - if (result == NULL) - { - errno = EFAULT; - return -1; - } + mp_limb mpn[(3 * sizeof (unsigned short int) + sizeof (mp_limb) - 1) + / sizeof (mp_limb)]; /* Compute next state. */ if (__drand48_iterate (xsubi, buffer) < 0) return -1; - *result = 0.0; - for (i = 4 / sizeof (unsigned short int); i >= 0; --i) - { - double factor = ldexp (1.0, (i - 6) * sizeof (unsigned short int)); + /* Build a 48-bit mpn containing the 48 random bits. */ + +#if BITS_PER_MP_LIMB == 64 + mpn[0] = (xsubi[0] << 32) | (xsubi[1] << 16) | xsubi[2]; +#elif BITS_PER_MP_LIMB == 32 + mpn[0] = (xsubi[1] << 16) | xsubi[2]; + mpn[1] = xsubi[0]; +#else + #error "BITS_PER_MP_LIMB value not handled" +#endif + + /* Shift them up so they are most significant bits of the fraction. */ + __mpn_lshift (mpn, mpn, sizeof mpn / sizeof mpn[0], DBL_MANT_DIG - 48); - *result += factor * (double) xsubi[i]; - } + /* Construct a positive double using those bits for the fractional part, + and a zero exponent so the resulting FP number is [0.0,1.0). */ + *result = __mpn_construct_double (mpn, 0, 0); return 0; } |