Hi,
As reported here:
<https://savannah.gnu.org/bugs/index.php?31464>
expt currently wrongly prints the results for any negative base
numbers. The attached patch (also attached with the bug tracker) has a
fix and also adds a test case.
This is my first patch to guile, so please correct me if I have done
something wrong. I will be happy to rework it. I am yet to recieve the
assignment papers from the FSF (but they have been despatched already
by the FSF), I will mail them back as soon as I get it.
thanks
--
Ramakrishnan
From c23939a1c2b7bfe1b3cf20abb6a7b431699281a1 Mon Sep 17 00:00:00 2001
From: Ramakrishnan Muthukrishnan <vu3...@gmail.com>
Date: Sun, 31 Oct 2010 23:22:52 +0530
Subject: [PATCH] Fix for bug #31464. expt needs to treat negative bases specially.
Also adding test-suite cases for expt.
* libguile/numbers.c: if base is negative, find the absolute value
of the base, find log and then later reapply the negative sign.
The bug was caused by the fact that log of a negative number is
undefined.
* 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 | 11 +++++++++++
test-suite/tests/numbers.test | 7 ++++++-
2 files changed, 17 insertions(+), 1 deletions(-)
diff --git a/libguile/numbers.c b/libguile/numbers.c
index fbc6cc8..07ae95d 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -5451,6 +5451,17 @@ SCM_DEFINE (scm_expt, "expt", 2, 0, 0,
{
return scm_from_double (pow (scm_to_double (x), scm_to_double (y)));
}
+ else if (scm_is_real (x) &&
+ scm_is_real (y) &&
+ (scm_to_double (x) < 0) &&
+ !SCM_FRACTIONP (y))
+ {
+ SCM x_abs;
+
+ x_abs = scm_abs (x);
+ return scm_product(scm_from_double (-1.0),
+ scm_exp (scm_product (scm_log (x_abs), y)));
+ }
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..3d53bbe 100644
--- a/test-suite/tests/numbers.test
+++ b/test-suite/tests/numbers.test
@@ -2892,7 +2892,12 @@
(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? 1.0000000000000002+1.7320508075688772i (expt -8 1/3)"
+ (eqv-loosely? 1.0000000000000002+1.7320508075688772i (expt -8 1/3))))
;;;
;;; asinh
--
1.7.2.3
