From 74e3f8b2531ee873c3555060d5b02791a325553a Mon Sep 17 00:00:00 2001
From: Romain Vimont <rom@rom1v.com>
Date: Fri, 27 Jan 2023 19:26:19 +0100
Subject: [PATCH] Add random util

Add a user-friendly tool to generate random numbers.
---
 app/meson.build     |  1 +
 app/src/util/rand.c | 24 ++++++++++++++++++++++++
 app/src/util/rand.h | 16 ++++++++++++++++
 3 files changed, 41 insertions(+)
 create mode 100644 app/src/util/rand.c
 create mode 100644 app/src/util/rand.h

diff --git a/app/meson.build b/app/meson.build
index cc465564..3ddd5a5d 100644
--- a/app/meson.build
+++ b/app/meson.build
@@ -37,6 +37,7 @@ src = [
     'src/util/net_intr.c',
     'src/util/process.c',
     'src/util/process_intr.c',
+    'src/util/rand.c',
     'src/util/strbuf.c',
     'src/util/str.c',
     'src/util/term.c',
diff --git a/app/src/util/rand.c b/app/src/util/rand.c
new file mode 100644
index 00000000..590e4ca4
--- /dev/null
+++ b/app/src/util/rand.c
@@ -0,0 +1,24 @@
+#include "rand.h"
+
+#include <stdlib.h>
+
+#include "tick.h"
+
+void sc_rand_init(struct sc_rand *rand) {
+    sc_tick seed = sc_tick_now(); // microsecond precision
+    rand->xsubi[0] = (seed >> 32) & 0xFFFF;
+    rand->xsubi[1] = (seed >> 16) & 0xFFFF;
+    rand->xsubi[2] = seed & 0xFFFF;
+}
+
+uint32_t sc_rand_u32(struct sc_rand *rand) {
+    // jrand returns a value in range [-2^31, 2^31]
+    // conversion from signed to unsigned is well-defined to wrap-around
+    return jrand48(rand->xsubi);
+}
+
+uint64_t sc_rand_u64(struct sc_rand *rand) {
+    uint32_t msb = sc_rand_u32(rand);
+    uint32_t lsb = sc_rand_u32(rand);
+    return ((uint64_t) msb << 32) | lsb;
+}
diff --git a/app/src/util/rand.h b/app/src/util/rand.h
new file mode 100644
index 00000000..262b0b9b
--- /dev/null
+++ b/app/src/util/rand.h
@@ -0,0 +1,16 @@
+#ifndef SC_RAND_H
+#define SC_RAND_H
+
+#include "common.h"
+
+#include <inttypes.h>
+
+struct sc_rand {
+    unsigned short xsubi[3];
+};
+
+void sc_rand_init(struct sc_rand *rand);
+uint32_t sc_rand_u32(struct sc_rand *rand);
+uint64_t sc_rand_u64(struct sc_rand *rand);
+
+#endif