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Sat Mar 16 20:58:43 1996 Roland McGrath <roland@charlie-brown.gnu.ai.mit.edu> 

* stdlib/erand48_r.c: Use FP division by powers of two to distribute
	short bits into double.
This commit is contained in:
Roland McGrath 1996-03-17 02:00:05 +00:00
parent 6025c399e9
commit 5aab07eb56
2 changed files with 13 additions and 24 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
Sat Mar 16 20:58:43 1996 Roland McGrath <roland@charlie-brown.gnu.ai.mit.edu>
* stdlib/erand48_r.c: Use FP division by powers of two to distribute
short bits into double.
Sat Mar 16 20:08:22 1996 David Mosberger-Tang <davidm@azstarnet.com>
* sysdeps/alpha/memchr.S: new file.

32
stdlib/erand48_r.c
View File

@ -18,45 +18,29 @@ not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include <stdlib.h>
#include "gmp.h"
#include "gmp-mparam.h"
#include <float.h>
#include <limits.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)
unsigned short int xsubi[3];
struct drand48_data *buffer;
double *result;
{
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;
/* Build a 48-bit mpn containing the 48 random bits. */
/* Construct a positive double with the 48 random bits distributed over
its fractional part so the resulting FP number is [0.0,1.0). */
#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];
#if USHRT_MAX == 65535
*result = ((double) xsubi[2] / (1ULL << 48) +
(double) xsubi[1] / (1ULL << 32) +
(double) xsubi[0] / (1ULL << 16));
#else
#error "BITS_PER_MP_LIMB value not handled"
# error Unsupported size of short int
#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);
/* 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;
}