From c6e4eee78947634b95cf7fc43ba500c4e4e7d65a Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Tue, 24 Sep 2024 19:02:03 +0200
Subject: [PATCH] Added `rnd` function.

---
 lib/std/math/math_random.c3 | 41 +++++++++++++++++++++++++++++--------
 releasenotes.md             |  1 +
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/lib/std/math/math_random.c3 b/lib/std/math/math_random.c3
index f5d2c4d4d..90d1952a6 100644
--- a/lib/std/math/math_random.c3
+++ b/lib/std/math/math_random.c3
@@ -32,29 +32,45 @@ macro void seed_entropy(random)
  * Get the next value between 0 and max (not including max).
  *
  * @require is_random(random)
+ * @require max > 0
  **/
 macro int next(random, int max)
 {
-	return (int)(next_double(random) * max);
+	if (max == 1) return 0;
+	return (int)(random.next_long() % (uint)max);
 }
 
 def DefaultRandom = Sfc64Random;
 
+tlocal Sfc64Random default_random @private;
+tlocal bool default_random_initialized @private = false;
+
+/**
+ * Seed the default random function.
+ */
+fn void srand(ulong seed) @builtin
+{
+	default_random.set_seed(@as_char_view(seed));
+	default_random_initialized = true;
+}
+
 /**
  * Get a default random value between 0 and max (not including max)
  **/
 fn int rand(int max) @builtin
 {
-	tlocal Sfc64Random default_random;
-	tlocal bool initialized = false;
-	if (!initialized)
-	{
-		seed_entropy(&default_random);
-		initialized = true;
-	}
+	init_default_random();
 	return next(&default_random, max);
 }
 
+
+fn double rnd() @builtin
+{
+	init_default_random();
+	ulong val = default_random.next_long() & (1UL << 53 - 1);
+	return val * 0x1.0p-53;
+}
+
 /**
  * Get 'true' or 'false'
  *
@@ -127,3 +143,12 @@ interface Random
 	fn uint128 next_int128();
 	fn void next_bytes(char[] buffer);
 }
+
+macro init_default_random() @local
+{
+	if (!default_random_initialized)
+	{
+		seed_entropy(&default_random);
+		default_random_initialized = true;
+	}
+}
diff --git a/releasenotes.md b/releasenotes.md
index d6a89eb37..2b5e620bc 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -64,6 +64,7 @@
 - Add support for the QOI format.
 - Add `io::read_new_fully` for reading to the end of a stream.
 - Add `io::wrap_bytes` for reading bytes with `io` functions.
+- Add `rnd` default random function.
 
 ## 0.6.2 Change list