60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
|
#include "clapack.h"
|
||
|
|
|
||
|
|
/* Subroutine */ int dlabad_(doublereal *small, doublereal *large)
|
||
|
|
{
|
||
|
|
/* Builtin functions */
|
||
|
|
double d_lg10(doublereal *), sqrt(doublereal);
|
||
|
|
|
||
|
|
|
||
|
|
/* -- LAPACK auxiliary routine (version 3.1) -- */
|
||
|
|
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
|
||
|
|
/* November 2006 */
|
||
|
|
|
||
|
|
/* .. Scalar Arguments .. */
|
||
|
|
/* .. */
|
||
|
|
|
||
|
|
/* Purpose */
|
||
|
|
/* ======= */
|
||
|
|
|
||
|
|
/* DLABAD takes as input the values computed by DLAMCH for underflow and */
|
||
|
|
/* overflow, and returns the square root of each of these values if the */
|
||
|
|
/* log of LARGE is sufficiently large. This subroutine is intended to */
|
||
|
|
/* identify machines with a large exponent range, such as the Crays, and */
|
||
|
|
/* redefine the underflow and overflow limits to be the square roots of */
|
||
|
|
/* the values computed by DLAMCH. This subroutine is needed because */
|
||
|
|
/* DLAMCH does not compensate for poor arithmetic in the upper half of */
|
||
|
|
/* the exponent range, as is found on a Cray. */
|
||
|
|
|
||
|
|
/* Arguments */
|
||
|
|
/* ========= */
|
||
|
|
|
||
|
|
/* SMALL (input/output) DOUBLE PRECISION */
|
||
|
|
/* On entry, the underflow threshold as computed by DLAMCH. */
|
||
|
|
/* On exit, if LOG10(LARGE) is sufficiently large, the square */
|
||
|
|
/* root of SMALL, otherwise unchanged. */
|
||
|
|
|
||
|
|
/* LARGE (input/output) DOUBLE PRECISION */
|
||
|
|
/* On entry, the overflow threshold as computed by DLAMCH. */
|
||
|
|
/* On exit, if LOG10(LARGE) is sufficiently large, the square */
|
||
|
|
/* root of LARGE, otherwise unchanged. */
|
||
|
|
|
||
|
|
/* ===================================================================== */
|
||
|
|
|
||
|
|
/* .. Intrinsic Functions .. */
|
||
|
|
/* .. */
|
||
|
|
/* .. Executable Statements .. */
|
||
|
|
|
||
|
|
/* If it looks like we're on a Cray, take the square root of */
|
||
|
|
/* SMALL and LARGE to avoid overflow and underflow problems. */
|
||
|
|
|
||
|
|
if (d_lg10(large) > 2e3) {
|
||
|
|
*small = sqrt(*small);
|
||
|
|
*large = sqrt(*large);
|
||
|
|
}
|
||
|
|
|
||
|
|
return 0;
|
||
|
|
|
||
|
|
/* End of DLABAD */
|
||
|
|
|
||
|
|
} /* dlabad_ */
|