Thanks again, Mark and Ludovic.
Attached is an updated patch.
thanks
--
Ramakrishnan
From a1dd2da8562ddeb2052f2994ad0302bcc8d5d1a2 Mon Sep 17 00:00:00 2001
From: Ramakrishnan Muthukrishnan <vu3...@gmail.com>
Date: Sun, 31 Oct 2010 23:22:52 +0530
Subject: [PATCH] Adding a case for `expt' when base is negative.
* libguile/numbers.c (scm_expt): Add a case when base is a
negative number. Also fix the bug for the case when exponent
is an inexact number.
* test-suite/tests/numbers.test ("expt"): Add tests for the cases
when base is an integer and exponent is an inexact number, base
is an integer and exponent is a rational number, base and
exponent are both inexact and so on.
---
libguile/numbers.c | 18 +++++++++++++++++-
test-suite/tests/numbers.test | 13 ++++++++++++-
2 files changed, 29 insertions(+), 2 deletions(-)
diff --git a/libguile/numbers.c b/libguile/numbers.c
index fbc6cc8..e4b03aa 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -5445,12 +5445,28 @@ 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;
+
+ /* 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.
+ */
+ 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..97c58c9 100644
--- a/test-suite/tests/numbers.test
+++ b/test-suite/tests/numbers.test
@@ -2892,7 +2892,18 @@
(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)))
+ (pass-if (eqv-loosely? (* -2742638075.5 -2742638075.5)
+ (expt -2742638075.5 2)))
+ (pass-if (eqv-loosely? 4.0 (expt -2.0 2.0)))
+ (pass-if (eqv-loosely? -0.125 (expt -2.0 -3.0)))
+ (pass-if (eqv-loosely? -0.125 (expt -2 -3.0)))
+ (pass-if (eqv-loosely? 0.25 (expt 2.0 -2.0)))
+ (pass-if (eqv-loosely? +i (expt -1 0.5)))
+ (pass-if (eqv-loosely? +i (expt -1 1/2)))
+ (pass-if (eqv-loosely? 1.0000000000000002+1.7320508075688772i (expt -8 1/3))))
;;;
;;; asinh
--
1.7.2.3
