squiggle.c

commit 32033b5c86201233f337e372698403e2d4dca399
parent 9e1d4ee6d4597a1f47b612168e7002b78cb3400a
Author: NunoSempere <nuno.sempere@protonmail.com>
Date:   Sun, 23 Jul 2023 12:53:46 +0200

stop using pow when possible

https://stackoverflow.com/questions/2940367/what-is-more-efficient-using-pow-to-square-or-just-multiply-it-with-itself

Diffstat:
M
examples/06_gamma_beta/example
 | 
0

M
squiggle.c
 | 
9
+++++----

2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/examples/06_gamma_beta/example b/examples/06_gamma_beta/example
Binary files differ.
diff --git a/squiggle.c b/squiggle.c
@@ -105,9 +105,9 @@ float sample_gamma(float alpha, uint64_t* seed)
                 v = 1.0 + c * x;
             } while (v <= 0.0);
 
-            v = pow(v, 3);
+            v = v * v * v; 
             u = sample_unit_uniform(seed);
-            if (u < 1.0 - 0.0331 * pow(x, 4)) { // Condition 1
+            if (u < 1.0 - 0.0331 * (x * x * x * x)) { // Condition 1
                 // the 0.0331 doesn't inspire much confidence
                 // however, this isn't the whole story
                 // by knowing that Condition 1 implies condition 2
@@ -115,7 +115,7 @@ float sample_gamma(float alpha, uint64_t* seed)
                 // i.e., of not using the logarithms
                 return d * v;
             }
-            if (log(u) < 0.5 * pow(x, 2) + d * (1.0 - v + log(v))) { // Condition 2
+            if (log(u) < 0.5 * (x * x) + d * (1.0 - v + log(v))) { // Condition 2
                 return d * v;
             }
         }
@@ -161,7 +161,8 @@ float array_std(float* array, int length)
     float mean = array_mean(array, length);
     float std = 0.0;
     for (int i = 0; i < length; i++) {
-        std += pow(array[i] - mean, 2.0);
+        std += (array[i] - mean);
+				std *= std;
     }
     std = sqrt(std / length);
     return std;