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-rw-r--r--ChangeLog5
-rw-r--r--Doc/Zsh/mod_mathfunc.yo2
-rw-r--r--Src/Modules/mathfunc.c9
-rw-r--r--Test/V03mathfunc.ztst6
-rw-r--r--configure.ac2
5 files changed, 22 insertions, 2 deletions
diff --git a/ChangeLog b/ChangeLog
index 8601ba508..09c2bba15 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,11 @@
 	infinitely in the attempt.  Update the $pipestatus stress test so
 	that it also exercises the oldjobtab repair.
 
+2013-10-26  Peter Stephenson  <p.w.stephenson@ntlworld.com>
+
+	* Jun T: 31902: rationalise gamma function in mathfunc for
+	consistency with various libraries and user expectations.
+
 2013-10-25  Peter Stephenson  <p.w.stephenson@ntlworld.com>
 
 	* 31890 (with Mikael's fixes in 31891): NEWS: add descriptions
diff --git a/Doc/Zsh/mod_mathfunc.yo b/Doc/Zsh/mod_mathfunc.yo
index dda4f36fd..5239da5f8 100644
--- a/Doc/Zsh/mod_mathfunc.yo
+++ b/Doc/Zsh/mod_mathfunc.yo
@@ -33,7 +33,7 @@ returns an integer.
 The function tt(signgam) takes no arguments, and returns an integer, which
 is the C variable of the same name, as described in manref(gamma)(3).  Note
 that it is therefore only useful immediately after a call to tt(gamma) or
-tt(lgamma).  Note also that `tt(signgam+LPAR()RPAR)' and `tt(signgam)' are
+tt(lgamma).  Note also that `tt(signgam+LPAR()RPAR())' and `tt(signgam)' are
 distinct expressions.
 
 The following functions take two floating point arguments: tt(copysign),
diff --git a/Src/Modules/mathfunc.c b/Src/Modules/mathfunc.c
index 04483b555..efadd86ff 100644
--- a/Src/Modules/mathfunc.c
+++ b/Src/Modules/mathfunc.c
@@ -340,7 +340,16 @@ math_func(char *name, int argc, mnumber *argv, int id)
       break;
 
   case MF_GAMMA:
+#ifdef HAVE_TGAMMA
+      retd = tgamma(argd);
+#else
+#ifdef HAVE_SIGNGAM
+      retd = lgamma(argd);
+      retd = signgam*exp(retd);
+#else /*XXX assume gamma(x) returns Gamma(x), not log(|Gamma(x)|) */
       retd = gamma(argd);
+#endif
+#endif
       break;
 
   case MF_HYPOT:
diff --git a/Test/V03mathfunc.ztst b/Test/V03mathfunc.ztst
index 069059da4..ab383db43 100644
--- a/Test/V03mathfunc.ztst
+++ b/Test/V03mathfunc.ztst
@@ -136,3 +136,9 @@ F:This test fails if your math library doesn't have erand48().
   done
   (( ok ))
 0:Test random number generator distributions are not grossly broken
+
+  float -F 5 g l
+  (( g = gamma(2), l = lgamma(2) ))
+  print $g, $l
+0:Test Gamma function gamma and lgamma
+>1.00000, 0.00000
diff --git a/configure.ac b/configure.ac
index c3debd8ad..c3093f20d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1222,7 +1222,7 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       getrlimit getrusage \
 	       setlocale \
 	       uname \
-	       signgam \
+	       signgam tgamma \
 	       putenv getenv setenv unsetenv xw\
 	       brk sbrk \
 	       pathconf sysconf \