add a function to compute log(n) for integer n

This commit adds the function ln() to compute log(n) for integer n. It uses a
lookup table for n < 100 to speed things up.

1 files changed, 23 insertions, 0 deletions

diff --git a/src/test.c b/src/test.c
index fa4256f..9976f1f 100644
--- a/src/test.c
+++ b/src/test.c
@@ -489,6 +489,28 @@ err:
     return 1;
 }
 
+int test_ln(char *err)
+{
+    /* Tests the lnfact() function. */
+    size_t i;
+    double x, expected;
+
+    for (i = 1; i < 1000; i++) {
+        x = ln(i);
+        expected = log(i);
+
+        if (!isclose(x, expected, 1e-9, 1e-9)) {
+            sprintf(err, "ln(%zu) returned %.5g, but expected %.5g", i, x, expected);
+            goto err;
+        }
+    }
+
+    return 0;
+
+err:
+    return 1;
+}
+
 struct tests {
     testFunction *test;
     char *name;
@@ -505,6 +527,7 @@ struct tests {
     {test_interp1d, "test_interp1d"},
     {test_kahan_sum, "test_kahan_sum"},
     {test_lnfact, "test_lnfact"},
+    {test_ln, "test_ln"},
 };
 
 int main(int argc, char **argv)