60 lines
1.8 KiB
C
60 lines
1.8 KiB
C
#include "f2c.h"
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/* Subroutine */ int dlabad_(doublereal *small, doublereal *large)
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{
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/* -- LAPACK auxiliary routine (version 2.0) --
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Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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Courant Institute, Argonne National Lab, and Rice University
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October 31, 1992
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Purpose
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=======
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DLABAD takes as input the values computed by SLAMCH for underflow and
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overflow, and returns the square root of each of these values if the
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log of LARGE is sufficiently large. This subroutine is intended to
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identify machines with a large exponent range, such as the Crays, and
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redefine the underflow and overflow limits to be the square roots of
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the values computed by DLAMCH. This subroutine is needed because
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DLAMCH does not compensate for poor arithmetic in the upper half of
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the exponent range, as is found on a Cray.
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Arguments
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=========
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SMALL (input/output) DOUBLE PRECISION
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On entry, the underflow threshold as computed by DLAMCH.
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On exit, if LOG10(LARGE) is sufficiently large, the square
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root of SMALL, otherwise unchanged.
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LARGE (input/output) DOUBLE PRECISION
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On entry, the overflow threshold as computed by DLAMCH.
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On exit, if LOG10(LARGE) is sufficiently large, the square
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root of LARGE, otherwise unchanged.
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=====================================================================
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If it looks like we're on a Cray, take the square root of
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SMALL and LARGE to avoid overflow and underflow problems. */
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/* Builtin functions */
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double d_lg10(doublereal *), sqrt(doublereal);
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if (d_lg10(large) > 2e3) {
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*small = sqrt(*small);
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*large = sqrt(*large);
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}
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return 0;
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/* End of DLABAD */
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} /* dlabad_ */
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