git.postgresql.org Git - postgresql.git/commitdiff

diff --git a/src/backend/utils/adt/float.c b/src/backend/utils/adt/float.c

index 3382b86ba0dcb2a33397856e0ef573057c4b5d29..b5147c9aa451ed303b8bdfd11a30fbe737f0778b 100644 (file)

--- a/src/backend/utils/adt/float.c

+++ b/src/backend/utils/adt/float.c

*

*

* IDENTIFICATION

- * $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.123 2006年03月11日 01:19:22 neilc Exp $

+ * $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.124 2006年04月24日 20:36:32 tgl Exp $

*

*-------------------------------------------------------------------------

*/

/* ========== PRIVATE ROUTINES ========== */

#ifndef HAVE_CBRT

+

static double

cbrt(double x)

{

int isneg = (x < 0.0);

- double tmpres = pow(fabs(x), (double) 1.0 / (double) 3.0);

+ double absx = fabs(x);

+ double tmpres = pow(absx, (double) 1.0 / (double) 3.0);

+

+ /*

+ * The result is somewhat inaccurate --- not really pow()'s fault,

+ * as the exponent it's handed contains roundoff error. We can improve

+ * the accuracy by doing one iteration of Newton's formula. Beware of

+ * zero input however.

+ */

+ if (tmpres > 0.0)

+ tmpres -= (tmpres - absx/(tmpres*tmpres)) / (double) 3.0;

return isneg ? -tmpres : tmpres;

}