Update xorshift PRNG

CHANGELOG.md

@@ -15,6 +15,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `wpSip24Hasher128IO`, `wpSip48Hasher128IO`, `wpSip24Hasher64IO` and `wpSip48Hasher64IO` to setup the siphash IO structs for the different variants
 - `wpSipHasher128` and `wpSipHasher64` implementation for the 128 and 64 variants of siphash
 - Add `wpU8Const`, `wpU16Const`, `wpU32Const`, `wpU64Const`, `wpI8Const`, `wpI16Const`, `wpI32Const`, and `wpI64Const`
+- `wpPrngXorshiftInitWithSeed` to allow for user control with PRNG
+
+### Changed
+
+- Switched to using `wpMiscUtilsRotl64` in `xorshift`
 
 ## [2.4.0] - 2026-08-30
 

src/prng/xorshift/xorshift.c

@@ -4,6 +4,7 @@
 #include "../../common/aliases/aliases.h"
 #include "../../common/assert/assert.h"
 #include "../../common/platform/platform.h"
+#include "../../common/misc/misc_utils.h"
 #include <stdlib.h>
 #include <time.h>
 
@@ -12,16 +13,19 @@ struct SplitMix64State {
 	u64 seed;
 };
 
-wp_intern u64 rol64(u64 x, u64 bits);
 wp_intern u64 split_mix_64(SplitMix64State *state);
-wp_intern void seed_os_generator(void);
+wp_intern void seed_os_generator(u64 seed);
 wp_intern u64 generate_random_number(void);
 
 WpXor256State wpPrngXorshiftInit(void) {
+	return wpPrngXorshiftInitWithSeed(0);
+}
+
+WpXor256State wpPrngXorshiftInitWithSeed(u64 seed) {
 	wp_persist b8 seeded = false;
 	if (!seeded) {
 		seeded = true;
-		seed_os_generator();
+		seed_os_generator(seed);
 	}
 
 	SplitMix64State sm64 = {.seed = generate_random_number()};
@@ -46,7 +50,7 @@ u64 wpPrngXorshift256(WpXor256State *state) {
 }
 
 u64 wpPrngXorshift256ss(WpXor256State *state) {
-	const u64 result = rol64(state->z * 5, 7) * 9;
+	const u64 result = wpMiscUtilsRotl64(state->z * 5, 7) * 9;
 	const u64 t = state->z << 17;
 
 	state->y ^= state->w;
@@ -55,7 +59,7 @@ u64 wpPrngXorshift256ss(WpXor256State *state) {
 	state->w ^= state->x;
 
 	state->y ^= t;
-	state->x = rol64(state->x, 45);
+	state->x = wpMiscUtilsRotl64(state->x, 45);
 
 	return result;
 }
@@ -70,15 +74,11 @@ u64 wpPrngXorshift256p(WpXor256State *state) {
 	state->w ^= state->x;
 
 	state->y ^= t;
-	state->x  = rol64(state->x, 45);
+	state->x  = wpMiscUtilsRotl64(state->x, 45);
 
 	return result;
 }
 
-wp_intern u64 rol64(u64 x, u64 bits) {
-	return (x << bits) | (x >> (64 - bits));
-}
-
 wp_intern u64 split_mix_64(SplitMix64State *state) {
 	state->seed += 0x9E3779B97f4A7C15;
 
@@ -91,24 +91,30 @@ wp_intern u64 split_mix_64(SplitMix64State *state) {
 
 #if defined(WP_PLATFORM_C) && WP_PLATFORM_C_VERSION >= WP_PLATFORM_C11_VERSION
 #ifdef WP_PLATFORM_POSIX
-wp_intern void seed_os_generator(void) {
+wp_intern void seed_os_generator(u64 seed) {
+	if (seed == 0) {
 		struct timespec ts = {0};
 		int result = clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
 		wpRuntimeAssert(result == 0, "Invalid seed value");
+		seed = (u64)ts.tv_nsec;
+	}
 
-	srand48(ts.tv_nsec);
+	srand48(seed);
 }
 
 wp_intern u64 generate_random_number(void) {
 	return lrand48();
 }
 #else
-wp_intern void seed_os_generator(void) {
+wp_intern void seed_os_generator(u64 seed) {
+	if (seed == 0) {
 		struct timespec ts = {0};
 		int result = timespec_get(&ts, TIME_UTC);
 		wpRuntimeAssert(result != 0, "Invalid seed value");
+		seed = (u64)ts.tv_nsec;
+	}
 
-	srand(ts.tv_nsec);
+	srand(seed);
 }
 
 wp_intern u64 generate_random_number(void) {
@@ -119,11 +125,14 @@ wp_intern u64 generate_random_number(void) {
 }
 #endif // !WP_PLATFORM_POSIX
 #else
-wp_intern void seed_os_generator(void) {
+wp_intern void seed_os_generator(u64 seed) {
+	if (seed == 0) {
 		time_t result = time(NULL);
 		wpRuntimeAssert(result != (time_t)(-1), "Invalid seed value");
+		seed = (u64)result;
+	}
 
-	srand(result);
+	srand(seed);
 }
 
 wp_intern u64 generate_random_number(void) {

src/prng/xorshift/xorshift.h

@@ -19,6 +19,7 @@ struct WpXor256State {
 };
 
 WpXor256State wpPrngXorshiftInit(void);
+WpXor256State wpPrngXorshiftInitWithSeed(u64 seed);
 u64 wpPrngXorshift256(WpXor256State *state);
 u64 wpPrngXorshift256ss(WpXor256State *state);
 u64 wpPrngXorshift256p(WpXor256State *state);