Re: fix for expt bug

[Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 48 bytes --]

Here is the updated patch.

thanks
Ramakrishnan

[-- Attachment #2: expt-fix.patch --]
[-- Type: text/x-patch, Size: 3066 bytes --]

From e320d79c8f3cd8b7ddcb9c2d13356e34a3346cfe Mon Sep 17 00:00:00 2001
From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sun, 31 Oct 2010 23:22:52 +0530
Subject: [PATCH] Fix for bug #31464. expt needs to treat negative bases specially.

* libguile/numbers.c: If base is negative, expt needs to find
  -x^n = (-1^n) * (|x|^n). We find x^n and then if n is odd, we
  also multiply the result with -1. These changes apply only for
  cases where n is an integer.

* test-suite/tests/numbers.test: Two new test cases for expt. For
  cases where the base is negative and the power to be raised is
  not an integer, the result should be a complex number.
---
 libguile/numbers.c            |   13 ++++++++++++-
 test-suite/tests/numbers.test |   15 ++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/libguile/numbers.c b/libguile/numbers.c
index fbc6cc8..4b81d98 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -5445,12 +5445,23 @@ SCM_DEFINE (scm_expt, "expt", 2, 0, 0,
 	    "Return @var{x} raised to the power of @var{y}.") 
 #define FUNC_NAME s_scm_expt
 {
-  if (scm_is_true (scm_exact_p (x)) && scm_is_integer (y))
+  if (scm_is_true (scm_exact_p (y)) && scm_is_integer (y))
     return scm_integer_expt (x, y);
   else if (scm_is_real (x) && scm_is_real (y) && scm_to_double (x) >= 0.0)
     {
       return scm_from_double (pow (scm_to_double (x), scm_to_double (y)));
     }
+  else if (scm_is_real (x) && scm_is_integer (y) && (scm_to_double (x) < 0))
+    {
+      double result;
+      
+      result = pow (-scm_to_double (x), scm_to_double (y));
+
+      if (scm_is_true (scm_odd_p (y)))
+        return scm_from_double (-result);
+      else
+        return scm_from_double (result);
+    }
   else
     return scm_exp (scm_product (scm_log (x), y));
 }
diff --git a/test-suite/tests/numbers.test b/test-suite/tests/numbers.test
index 3c3e14f..637449f 100644
--- a/test-suite/tests/numbers.test
+++ b/test-suite/tests/numbers.test
@@ -2892,7 +2892,20 @@
   (pass-if "(= 1 (expt 0 0))" (= 1 (expt 0 0)))
   (pass-if "(= 1 (expt 0 0.0))" (= 1 (expt 0 0.0)))
   (pass-if "(= 1 (expt 0.0 0))" (= 1 (expt 0.0 0)))
-  (pass-if "(= 1 (expt 0.0 0.0))" (= 1 (expt 0.0 0.0))))
+  (pass-if "(= 1 (expt 0.0 0.0))" (= 1 (expt 0.0 0.0)))
+  ;; tests for non zero values of base and exponent.
+  (pass-if "(eqv-loosely? -2742638075.5 (expt -2742638075.5 1))"
+            (eqv-loosely? -2742638075.5 (expt -2742638075.5 1)))
+  (pass-if "(eqv-loosely? 4.0 (expt -2.0 2.0))"
+           (eqv-loosely? 4.0 (expt -2.0 2.0)))
+  (pass-if "(eqv-loosely? -0.125 (expt -2.0 -3.0))"
+           (eqv-loosely? -0.125 (expt -2.0 -3.0)))
+  (pass-if "(eqv-loosely? -0.125 (expt -2 -3.0))"
+           (eqv-loosely? -0.125 (expt -2 -3.0)))
+  (pass-if "(eqv-loosely? 0.25 (expt 2.0 -2.0))"
+           (eqv-loosely? 0.25 (expt 2.0 -2.0)))
+  (pass-if "(eqv-loosely? 1.0000000000000002+1.7320508075688772i (expt -8 1/3))"
+            (eqv-loosely? 1.0000000000000002+1.7320508075688772i (expt -8 1/3))))
 
 ;;;
 ;;; asinh
-- 
1.7.2.3