[goffice] Doc fix.

[Morten Welinder <mortenw src gnome org>]

commit 0e97dac33e342d442b7bdc59e3afc80ee8f7f657
Author: Morten Welinder <terra gnome org>
Date:   Thu Dec 5 16:35:52 2013 -0500

    Doc fix.

 goffice/math/go-quad.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)
---
diff --git a/goffice/math/go-quad.c b/goffice/math/go-quad.c
index 0f27620..d63b529 100644
--- a/goffice/math/go-quad.c
+++ b/goffice/math/go-quad.c
@@ -782,6 +782,15 @@ SUFFIX(go_quad_atan_internal) (QUAD *res, const QUAD *x)
 
        g_return_if_fail (SUFFIX(fabs) (x->h) <= 1);
 
+       /*
+        * This follows "An Algorithm for Computing Logarithms
+        * and Arctangents" by B. C. Carlson in *Mathematics of
+        * Computation*, Volume 26, Number 118, April 1972.
+        *
+        * If need be we can do log, arcsin, arccos, arctanh,
+        * arcsinh, and arccosh we the same code.
+        */
+
        qrp = SUFFIX(go_quad_zero);
 
        dpk[0] = SUFFIX(go_quad_one);
@@ -809,7 +818,7 @@ SUFFIX(go_quad_atan_internal) (QUAD *res, const QUAD *x)
                SUFFIX(go_quad_div) (&qr, x, &dk[n]);
                
                SUFFIX(go_quad_sub) (&qrp, &qrp, &qr);
-               if (SUFFIX(fabs)(qrp.h) <= SUFFIX(ldexp) (SUFFIX(fabs)(qr.h), -100)) {
+               if (SUFFIX(fabs)(qrp.h) <= SUFFIX(ldexp) (SUFFIX(fabs)(qr.h), -2 * (DBL_MANT_DIG - 1))) {
                        converged = TRUE;
                        break;
                }