From 8e20b8636523b488e1cdaae500dceefb44fa7012 Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Fri, 1 Oct 2021 16:06:13 +0100
Subject: [PATCH] crand::_sample() uniformly distributes between 0..1
MIME-Version: 1.0
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Fortune for cpprng's current commit: Blessing − 吉
---
 include/rng/crand.h |  4 ++--
 src/rng/crand.c     | 13 ++++++++++++-
 src/rng/crand.cpp   | 11 +++++------
 src/rng/crand.h     |  1 +
 4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/include/rng/crand.h b/include/rng/crand.h
index 21034ef..0466dea 100644
--- a/include/rng/crand.h
+++ b/include/rng/crand.h
@@ -18,7 +18,7 @@ namespace rng
 
 		inline ~crand(){}
 
-		inline i64 next_i64() override { return _sample_raw(); }
+		inline i64 next_i64() override { return _sample_int(); }
 		u64 next_u64() override;
 	protected:
 		inline constexpr i64 _max_i64() const override { return RANGE_MAX; }
@@ -31,6 +31,6 @@ namespace rng
 		mem::aligned_ptr<_opaque, _deleter> _state;
 
 		explicit crand(_opaque* raw);
-		i64 _sample_raw();
+		i64 _sample_int();
 	};
 }
diff --git a/src/rng/crand.c b/src/rng/crand.c
index 4540a54..d4501ae 100644
--- a/src/rng/crand.c
+++ b/src/rng/crand.c
@@ -11,7 +11,10 @@ typedef unsigned short uint48_t[3];
 
 struct jr_state
 {
-	long result;
+	union {
+		long result;
+		double fresult;
+	};
 	struct drand48_data data;
 	union {
 		unsigned short xsubi[3];
@@ -59,6 +62,14 @@ long _jr_proc(struct jr_state* restrict state)
 	return state->result;
 }
 
+//TODO: a version of _jr_proc that uses use `erand48_r()` to return between 0..1.0 for _sample()
+
+double _jr_procf(struct jr_state* restrict state)
+{
+	erand48_r(_jr_st_resolv(state), &state->data, &state->fresult);
+	return state->fresult;
+}
+
 struct jr_state* _jr_alloc()
 {
 	struct jr_state* bx = aligned_alloc(_Alignof(struct jr_state), sizeof(struct jr_state));
diff --git a/src/rng/crand.cpp b/src/rng/crand.cpp
index 50314ce..c75b1bf 100644
--- a/src/rng/crand.cpp
+++ b/src/rng/crand.cpp
@@ -26,15 +26,14 @@ namespace rng
 	crand::crand(u64 seed) : crand(reinterpret_cast<_opaque*>(_jr_new(seed))){}
 	crand::crand() : crand(0xabad1dea){}
 
-	i64 crand::_sample_raw() { return _jr_proc(reinterpret_cast<jr_state*>(_state.get_ptr())); }
-
-	//TODO: properly implemet this f64 crand::_sample() { return (f64)std::bit_cast<u64>(_sample_raw()) / (f64)UINT64_MAX; }
+	i64 crand::_sample_int() { return _jr_proc(reinterpret_cast<jr_state*>(_state.get_ptr())); } //RANGE_MIN..=RANGE_MAX
+	f64 crand::_sample() { return _jr_procf(reinterpret_cast<jr_state*>(_state.get_ptr())); }    //0..1
 
 	// Overrides //
-	u64 crand::next_u64() { return std::bit_cast<u64>(std::abs(_sample_raw()) & INT32_MAX); } // remove sign bit because it messes with the range.
+	u64 crand::next_u64() { return std::bit_cast<u64>(std::abs(_sample_int()) & INT32_MAX); }
+	// next_i/u64(max) overrides not nessicary, the impl would be same as base. same with array next_*(p, n) overrides
 
-	//TODO: Implementing next_i64(i64 max) should be trivial. the man page for drand48 shows its output range, just map that range to `0..=max`
-	//TODO: make the default range for all non-bounded `next_i/u*` the same range as drand48's. If that's too big for the integer type, scale it down.
+	//TODO: next_bytes(), next_v*()
 }
 
 void rng_test()
diff --git a/src/rng/crand.h b/src/rng/crand.h
index af70e67..2da1611 100644
--- a/src/rng/crand.h
+++ b/src/rng/crand.h
@@ -15,6 +15,7 @@ struct jr_state;
 
 void _jr_seed(struct jr_state* restrict state, unsigned long with);
 long _jr_proc(struct jr_state* restrict state);
+double _jr_procf(struct jr_state* restrict state);
 struct jr_state* _jr_alloc();
 void _jr_free(struct jr_state* restrict state);