From 17be975d3afbff837ea621470f8a093c0090c5c8 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bruce@bruce-hill.com>
Date: Sat, 3 Aug 2024 16:23:28 -0400
Subject: Fix integer random functions so they correctly handle all
 representable ranges

---
 builtins/integers.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

(limited to 'builtins/integers.c')

diff --git a/builtins/integers.c b/builtins/integers.c
index ef9b5df4..d50c6573 100644
--- a/builtins/integers.c
+++ b/builtins/integers.c
@@ -51,14 +51,22 @@
         } \
         return bit_array; \
     } \
-    public c_type KindOfInt ## $random(int64_t min, int64_t max) { \
-        if (min > max) fail("Random min (%ld) is larger than max (%ld)", min, max); \
-        if (min < (int64_t)min_val) fail("Random min (%ld) is smaller than the minimum "#KindOfInt" value", min); \
-        if (max > (int64_t)max_val) fail("Random max (%ld) is smaller than the maximum "#KindOfInt" value", max); \
-        int64_t range = max - min; \
-        if (range > UINT32_MAX) fail("Random range (%ld) is larger than the maximum allowed (%ld)", range, UINT32_MAX); \
-        uint32_t r = arc4random_uniform((uint32_t)range); \
-        return min + (c_type)r; \
+    public c_type KindOfInt ## $random(c_type min, c_type max) { \
+        if (min > max) fail("Random minimum value (%ld) is larger than the maximum value (%ld)", min, max); \
+        if (min == max) return min; \
+        if (min == min_val && max == max_val) { \
+            c_type r; \
+            arc4random_buf(&r, sizeof(r)); \
+            return r; \
+        } \
+        uint64_t range = (uint64_t)max - (uint64_t)min + 1; \
+        uint64_t min_r = -range % range; \
+        uint64_t r; \
+        for (;;) { \
+            arc4random_buf(&r, sizeof(r)); \
+            if (r >= min_r) break; \
+        } \
+        return (c_type)((uint64_t)min + (r % range)); \
     } \
     public c_type KindOfInt ## $from_text(CORD text, CORD *the_rest) { \
         const char *str = CORD_to_const_char_star(text); \
-- 
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