From b59c0671d287a9552295c980680f005ee77786ec Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Fri, 1 Oct 2021 15:58:52 +0100
Subject: [PATCH] Added ranges to Random base.
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Added crand::RANGE_MIN/MAX, overriden required base ranges to point to them.

crand::next_u64() returns within this range but discards the negative result

Fortune for cpprng's current commit: Small blessing − 小吉
---
 include/rng.h       | 13 +++++++++++--
 include/rng/crand.h |  7 +++++++
 src/rng.cpp         |  2 ++
 src/rng/crand.cpp   | 11 ++++++++++-
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/include/rng.h b/include/rng.h
index 06c6eb7..0741886 100644
--- a/include/rng.h
+++ b/include/rng.h
@@ -78,8 +78,8 @@ struct Random
 
 	virtual bool next_bool();
 
-#define NDEF(t, M) inline virtual t next_ ## t() { return next_ ## t(M); }
-#define NDEFF(n) NDEF(i ## n, INT ## n ## _MAX) NDEF(u ## n, UINT ## n ## _MAX)
+#define NDEF(t) inline virtual t next_ ## t() { return next_ ## t(_max_ ## t()); }
+#define NDEFF(n) NDEF(i ## n) NDEF(u ## n)
 	NDEFF(8)
 	NDEFF(16)
 	NDEFF(32)
@@ -151,6 +151,15 @@ struct Random
 	template<typename T>
 	inline iterator<T> iter() { return iterator(*this); }  //TODO: An iterator that yields `next<T>()` forever.
 protected:
+	//TODO: Should we have _min_* functions too? or just continue to use 0 as the lower bound for next_*(..max)? I think use 0...
+#define MAX(T, M) constexpr inline virtual T _max_ ## T() const { return M; }
+#define MAXX(n) MAX(u ## n, UINT ## n ## _MAX) MAX(i ## n, INT ## n ## _MAX)
+	MAXX(8)
+	MAXX(16)
+	MAXX(32)
+	MAXX(64)
+#undef MAXX
+#undef MAX	
 	//constexpr inline virtual i8 _max() const { return 100; } // use limits.h stuff instead.
 
 	// Vectorised versions of `next_bytes()`. These will fall back to that if they are not overriden, but if the implementation has a more efficient way of generating 4/8 bytes of random data it should override these.
diff --git a/include/rng/crand.h b/include/rng/crand.h
index 8ad60d0..21034ef 100644
--- a/include/rng/crand.h
+++ b/include/rng/crand.h
@@ -9,6 +9,10 @@ namespace rng
 {
 	struct crand final : public Random
 	{
+		// This range is inclusive
+		constexpr static inline i64 RANGE_MIN = - (1L << 31);
+		constexpr static inline i64 RANGE_MAX =   (1L << 31) - 1;
+
 		crand();
 		crand(u64 seed);
 
@@ -17,6 +21,9 @@ namespace rng
 		inline i64 next_i64() override { return _sample_raw(); }
 		u64 next_u64() override;
 	protected:
+		inline constexpr i64 _max_i64() const override { return RANGE_MAX; }
+		inline constexpr u64 _max_u64() const override { return (u64)RANGE_MAX; }
+		// the rest of the base `_max_*` functions are valid, as they will always be equal to or less than INT32_MAX (the upper bound of dr48.) 
 		f64 _sample() override;
 	private:
 		struct _opaque;
diff --git a/src/rng.cpp b/src/rng.cpp
index 7e523ee..d5cf204 100644
--- a/src/rng.cpp
+++ b/src/rng.cpp
@@ -46,3 +46,5 @@ N_INTS
 
 #undef NEXTT
 #undef NEXT
+
+//TODO: next_*(min, max)
diff --git a/src/rng/crand.cpp b/src/rng/crand.cpp
index 6c8e382..ef0fb39 100644
--- a/src/rng/crand.cpp
+++ b/src/rng/crand.cpp
@@ -8,6 +8,14 @@
 #include <rng/crand.h>
 #include "crand.h"
 
+// Note: the output of drand48 is uniform between INT32_MIN..=INT32_MAX (inclusive)
+
+constexpr const i64 _J_RANGE_MIN = (i64)INT32_MIN;
+constexpr const i64 _J_RANGE_MAX = (i64)INT32_MAX;
+
+static_assert(_J_RANGE_MIN == rng::crand::RANGE_MIN);
+static_assert(_J_RANGE_MAX == rng::crand::RANGE_MAX);
+
 namespace rng
 {	
 	void crand::_deleter::delete_object(_opaque** state) { _jr_free(reinterpret_cast<jr_state*>(*state)); *state = nullptr; }
@@ -22,7 +30,8 @@ namespace rng
 	//TODO: properly implemet this f64 crand::_sample() { return (f64)std::bit_cast<u64>(_sample_raw()) / (f64)UINT64_MAX; }
 
 	// Overrides //
-	u64 crand::next_u64() { return std::bit_cast<u64>(_sample_raw()); }
+	u64 crand::next_u64() { return std::bit_cast<u64>(_sample_raw() & INT32_MAX); } // remove sign bit because it messes with the range.
+
 	//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.
 }