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[PATCH] fix for accuracy problem in atan2f

This patch fixes a problem with the accuracy of atan2f by changing to use the round-to-nearest value of pi. See for a better description of the issue. A similar change was made to glibc back in July 1997, but there was a typo in that change, for which I have just submitted a patch: See my glibc patch if you want a testcase to demonstrate the problem.

2005-07-20  Bob Wilson  <>
           Darin Petkov <>

* libm/math/ef_atan2.c (pi, pi_lo): Use round-to-nearest value of pi.

Index: libm/math/ef_atan2.c
RCS file: /cvs/src/src/newlib/libm/math/ef_atan2.c,v
retrieving revision 1.2
diff -u -r1.2 ef_atan2.c
--- libm/math/ef_atan2.c	4 Apr 2001 13:30:59 -0000	1.2
+++ libm/math/ef_atan2.c	20 Jul 2005 15:43:14 -0000
@@ -25,8 +25,8 @@
 zero  = 0.0,
 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
-pi      = 3.1415925026e+00, /* 0x40490fda */
-pi_lo   = 1.5099578832e-07; /* 0x34222168 */
+pi      = 3.1415927410e+00,  /* 0x40490fdb */
+pi_lo   = -8.7422776573e-08; /* 0xb3bbbd2e */
 #ifdef __STDC__
 	float __ieee754_atan2f(float y, float x)

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