[gnumeric] BETA: fix special case.

[Morten Welinder <mortenw src gnome org>]

commit cbcee7938eca1a7152e85024048a59e8efcd7dad
Author: Morten Welinder <terra gnome org>
Date:   Thu Mar 19 08:44:29 2015 -0400

    BETA: fix special case.
    
    Handle removable pole when the arguments sum to a non-negative integer
    but neither of them is.

 ChangeLog      |    5 +++++
 NEWS           |    1 +
 src/sf-gamma.c |    9 +++++++--
 3 files changed, 13 insertions(+), 2 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 92c5331..d8f58b2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2015-03-19  Morten Welinder  <terra gnome org>
+
+       * src/sf-gamma.c (qbetaf): Return zero as result when a+b is a
+       non-positive integer, but neither a nor b is.
+
 2015-03-07  Morten Welinder  <terra gnome org>
 
        * src/xml-sax-write.c: Use new go_xml_out_add_double.
diff --git a/NEWS b/NEWS
index d49a3e8..b45266e 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,7 @@ Morten:
        * Fix xlsx title export problem.
        * Improve test suite.
        * Actually implement DECIMAL.
+       * Fix BETA problem with special case.
 
 --------------------------------------------------------------------------
 Gnumeric 1.12.21
diff --git a/src/sf-gamma.c b/src/sf-gamma.c
index 87e8dec..aa283d6 100644
--- a/src/sf-gamma.c
+++ b/src/sf-gamma.c
@@ -506,10 +506,15 @@ qbetaf (gnm_float a, gnm_float b, GnmQuad *mant, int *exp2)
 
        if (gnm_isnan (ab) ||
            (a <= 0 && a == gnm_floor (a)) ||
-           (b <= 0 && b == gnm_floor (b)) ||
-           (ab <= 0 && ab == gnm_floor (ab)))
+           (b <= 0 && b == gnm_floor (b)))
                return 2;
 
+       if (ab <= 0 && ab == gnm_floor (ab)) {
+               gnm_quad_init (mant, 0);
+               *exp2 = 0;
+               return 0;
+       }
+
        if (!qgammaf (a, &ma, &ea) &&
            !qgammaf (b, &mb, &eb) &&
            !qgammaf (ab, &mab, &eab)) {