From a40d1d504a6eeb457c5c8a1d39b93301d9c34f28 Mon Sep 17 00:00:00 2001
From: Jeronimo Pellegrini <j_p@aleph0.info>
Date: Thu, 6 Apr 2023 09:38:09 -0300
Subject: [PATCH] Make (log x 0) return 0 (as per the spec)

The CL spec says that "If base is zero, log returns zero."  But ECL
was not checking for zero, so a divide by zero error was generated.
This patch makes it return zero when the base is zero:

> (log  1 0)

0
> (log 1/2 0)

0
> (log #C(2 1) 0)

0
> (log 2 0.0)

0
---
 src/c/numbers/log.d | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/c/numbers/log.d b/src/c/numbers/log.d
index 7745a6472..6ff500752 100644
--- a/src/c/numbers/log.d
+++ b/src/c/numbers/log.d
@@ -384,6 +384,9 @@ MATH_DEF_DISPATCH1(log1_long_precision, @[log], @[number],
 cl_object
 ecl_log2(cl_object x, cl_object y)
 {
+  /* The spec says "If base is zero, log returns zero" */
+  if (ecl_zerop(x)) return ecl_make_fixnum(0);
+
   cl_type tx = ecl_t_of(x);
   cl_type ty = ecl_t_of(y);
   /* Prevent loss of precision from intermediate single float results */
-- 
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