From 88177a3248d15a44f442f7e52ecfd61645391d7b Mon Sep 17 00:00:00 2001
From: tylo <tylo@norceresearch.no>
Date: Fri, 7 Aug 2020 17:47:38 +0200
Subject: Added i64 uniform distribution range. in crandom.h

---
 examples/rngtest.c |  8 ++++++--
 stc/crandom.h      | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/examples/rngtest.c b/examples/rngtest.c
index ca037292..66e5f0c8 100644
--- a/examples/rngtest.c
+++ b/examples/rngtest.c
@@ -12,7 +12,12 @@ int main(void)
 {
     clock_t difference, before;
     uint64_t v;
-    printf("start\n");
+    
+    crandom_eng64_t sfc = crandom_eng64_init(time(NULL));
+    crandom_distrib_i64_t d10 = crandom_uniform_i64_init(10, 20);
+    
+    for (int i=0; i<30; ++i) printf("%02zd ", crandom_uniform_i64(&sfc, d10)); 
+    puts("");
 
     crandom_eng32_t pcg = crandom_eng32_init(time(NULL));
     before = clock(); \
@@ -23,7 +28,6 @@ int main(void)
     difference = clock() - before;
     printf("pcg32: %.02f, %zu\n", (float) difference / CLOCKS_PER_SEC, v);
 
-    crandom_eng64_t sfc = crandom_eng64_init(time(NULL));
     before = clock(); \
     v = 0;
     for (size_t i=0; i<NN; i++) {
diff --git a/stc/crandom.h b/stc/crandom.h
index b73dd11b..cd6c98cd 100644
--- a/stc/crandom.h
+++ b/stc/crandom.h
@@ -73,6 +73,7 @@ STC_INLINE float crandom_uniform_f32(crandom_eng32_t* rng, crandom_distrib_f32_t
 
 
 typedef struct {uint64_t state[4];} crandom_eng64_t;
+typedef struct {int64_t offset, range;} crandom_distrib_i64_t;
 typedef struct {double offset, range;} crandom_distrib_f64_t;
 
 /* 64 bit random number generator engine */
@@ -89,6 +90,21 @@ STC_INLINE double crandom_f64(crandom_eng64_t* rng) {
     return u.f - 1.0;
 }
 
+/* int random number generator in range [low, high] */
+STC_INLINE crandom_distrib_i64_t crandom_uniform_i64_init(int64_t low, int64_t high) {
+    crandom_distrib_i64_t dist = {low, high - low + 1}; return dist;
+}
+STC_INLINE int64_t crandom_uniform_i64(crandom_eng64_t* rng, crandom_distrib_i64_t dist) {
+#if defined(__SIZEOF_INT128__)
+    return dist.offset + (int64_t) (((__uint128_t) crandom_i64(rng) * dist.range) >> 64);
+#elif defined(_MSC_VER)
+    int64_t hi; _mul128(crandom_i64(rng) >> 1, dist.range << 1, &hi); return dist.offset + hi;
+#else
+    return dist.offset + (((uint32_t) crandom_i64(rng) * dist.range) >> 32); // range up to 2^32
+    //return dist.offset + crandom_i64(rng) % dist.range; // slow
+#endif
+}
+
 STC_INLINE crandom_distrib_f64_t crandom_uniform_f64_init(double low, double high) {
     crandom_distrib_f64_t dist = {low, high - low}; return dist;
 }
-- 
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