expt: zero exponent yields 1.0.

* arith.c (expt): NUM-FLNUM, FLNUM-NUM and FLNUM-FLNUM cases
ensure that if the expontent is zero, the return value is
1.0. Implementations of pow do this, but ISO C doesn't require it.

* txr.1: Now documented.

2 files changed, 9 insertions, 0 deletions

diff --git a/arith.c b/arith.c
index fad3e15b..32f3da44 100644
--- a/arith.c
+++ b/arith.c
@@ -2468,6 +2468,8 @@ tail:
       cnum a = c_n(anum);
       double b = c_flo(bnum, self);
 
+      if (b == 0.0)
+        return flo(1.0);
       if (a == 0 && b < 0)
         goto divzero;
       return flo(pow(a, b));
@@ -2477,6 +2479,8 @@ tail:
       double a = c_flo(anum, self);
       cnum b = c_n(bnum);
 
+      if (b == 0)
+        return flo(1.0);
       if (a == 0 && b < 0)
         goto divzero;
       return flo(pow(a, b));
@@ -2486,6 +2490,8 @@ tail:
     {
       double a = c_flo(anum, self);
       double b = c_flo(bnum, self);
+      if (b == 0.0)
+        return flo(1.0);
       if (a == 0 && b < 0)
         goto divzero;
       return flo(pow(a, b));
diff --git a/txr.1 b/txr.1
index cf6289d3..4e97200a 100644
--- a/txr.1
+++ b/txr.1
@@ -48549,6 +48549,9 @@ operand is converted to a float, and a floating point exponentiation
 is performed. Exponentiation that would produce a complex number is
 not supported.
 
+If the exponent is zero, then the return value is 1.0 if at least one operand
+is floating-point, otherwise 1.
+
 The
 .code sqrt
 function produces a floating-point square root of