From 4069cf570107133c84bbb772625db18741f25598 Mon Sep 17 00:00:00 2001
From: Christopher Haster <geky@geky.net>
Date: Thu, 2 Nov 2023 12:16:42 -0500
Subject: [PATCH] Tweaked test/bench prng to convert 0 -> -1

Like many prngs, xorshift breaks down when the internal state is 0. The
common fix is to explicitly check for this and replace with a 1 when
this happens (usually when seeding, in this API we have to check every
update, this is less efficient but I don't think we really care).

As a slight tweak, this now checks for 0 but replaces it with -1. This
makes seed=0 different from seed=1, which is nice when using
seed=range(0,n) in tests/benches.
---
 runners/bench_runner.c | 5 +++++
 runners/test_runner.c  | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/runners/bench_runner.c b/runners/bench_runner.c
index 44a3637f..384995d9 100644
--- a/runners/bench_runner.c
+++ b/runners/bench_runner.c
@@ -587,6 +587,11 @@ uint32_t bench_prng(uint32_t *state) {
     // A simple xorshift32 generator, easily reproducible. Keep in mind
     // determinism is much more important than actual randomness here.
     uint32_t x = *state;
+    // must be non-zero, use uintmax here so that seed=0 is different
+    // from seed=1 and seed=range(0,n) makes a bit more sense
+    if (x == 0) {
+        x = -1;
+    }
     x ^= x << 13;
     x ^= x >> 17;
     x ^= x << 5;
diff --git a/runners/test_runner.c b/runners/test_runner.c
index 4e1eeb7f..ba9ca95a 100644
--- a/runners/test_runner.c
+++ b/runners/test_runner.c
@@ -603,6 +603,11 @@ uint32_t test_prng(uint32_t *state) {
     // A simple xorshift32 generator, easily reproducible. Keep in mind
     // determinism is much more important than actual randomness here.
     uint32_t x = *state;
+    // must be non-zero, use uintmax here so that seed=0 is different
+    // from seed=1 and seed=range(0,n) makes a bit more sense
+    if (x == 0) {
+        x = -1;
+    }
     x ^= x << 13;
     x ^= x >> 17;
     x ^= x << 5;