[gnumeric] R.PBINOM: fix p==1 and n==0 cases.

[Morten Welinder <mortenw src gnome org>]

commit ca00c7901a145383a17bcf49c15be2908baab68f
Author: Morten Welinder <terra gnome org>
Date:   Fri Apr 12 13:34:20 2013 -0400

    R.PBINOM: fix p==1 and n==0 cases.

 ChangeLog      |    2 ++
 NEWS           |    1 +
 src/mathfunc.c |    2 +-
 3 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index b85d11a..139dbc2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,8 @@
 
        * src/mathfunc.c (gnm_owent): Fix a==1 special case.  Part of
        #697850.
+       (pnbinom): Allow prob==1 (already fixed in R) and n==0 (now
+       reported to R).
 
 2013-04-11  Morten Welinder  <terra gnome org>
 
diff --git a/NEWS b/NEWS
index 950c95a..fb7bba8 100644
--- a/NEWS
+++ b/NEWS
@@ -35,6 +35,7 @@ Morten:
        * Ensure full precision for complex numbers.  [#697634]
        * Fix parsing of 'Sheet1!#REF!' as used by XL.  [#683494]
        * New function NT_OMEGA.
+       * Fix minor R.PBINOM problems.
 
 --------------------------------------------------------------------------
 Gnumeric 1.12.1
diff --git a/src/mathfunc.c b/src/mathfunc.c
index 7d3dc11..5b52a7e 100644
--- a/src/mathfunc.c
+++ b/src/mathfunc.c
@@ -2998,7 +2998,7 @@ gnm_float pnbinom(gnm_float x, gnm_float n, gnm_float p, gboolean lower_tail, gb
        return x + n + p;
     if(!gnm_finite(n) || !gnm_finite(p))       ML_ERR_return_NAN;
 #endif
-    if (n <= 0 || p <= 0 || p >= 1)    ML_ERR_return_NAN;
+    if (n < 0 || p <= 0 || p > 1)      ML_ERR_return_NAN;
 
     x = gnm_fake_floor(x);
     if (x < 0) return R_DT_0;