Merge pull request #3997 from endragor/portable-mersenne

mersenne.nim public procs are no longer platform-dependent

2 files changed, 18 insertions, 13 deletions

diff --git a/lib/pure/mersenne.nim b/lib/pure/mersenne.nim
index ae0845714..afa343086 100644
--- a/lib/pure/mersenne.nim
+++ b/lib/pure/mersenne.nim
@@ -5,29 +5,31 @@ type
 
 {.deprecated: [TMersenneTwister: MersenneTwister].}
 
-proc newMersenneTwister*(seed: int): MersenneTwister =
+proc newMersenneTwister*(seed: uint32): MersenneTwister =
   result.index = 0
-  result.mt[0]= uint32(seed)
+  result.mt[0] = seed
   for i in 1..623'u32:
-    result.mt[i]= (0x6c078965'u32 * (result.mt[i-1] xor (result.mt[i-1] shr 30'u32)) + i)
+    result.mt[i] = (0x6c078965'u32 * (result.mt[i-1] xor (result.mt[i-1] shr 30'u32)) + i)
 
 proc generateNumbers(m: var MersenneTwister) =
   for i in 0..623:
-    var y = (m.mt[i] and 0x80000000'u32) + (m.mt[(i+1) mod 624] and 0x7fffffff'u32)
+    var y = (m.mt[i] and 0x80000000'u32) +
+            (m.mt[(i+1) mod 624] and 0x7fffffff'u32)
     m.mt[i] = m.mt[(i+397) mod 624] xor uint32(y shr 1'u32)
     if (y mod 2'u32) != 0:
-     m.mt[i] = m.mt[i] xor 0x9908b0df'u32
+      m.mt[i] = m.mt[i] xor 0x9908b0df'u32
 
-proc getNum*(m: var MersenneTwister): int =
+proc getNum*(m: var MersenneTwister): uint32 =
+  ## Returns the next pseudo random number ranging from 0 to high(uint32)
   if m.index == 0:
     generateNumbers(m)
-  var y = m.mt[m.index]
-  y = y xor (y shr 11'u32)
-  y = y xor ((7'u32 shl y) and 0x9d2c5680'u32)
-  y = y xor ((15'u32 shl y) and 0xefc60000'u32)
-  y = y xor (y shr 18'u32)
-  m.index = (m.index+1) mod 624
-  return int(y)
+  result = m.mt[m.index]
+  m.index = (m.index + 1) mod m.mt.len
+
+  result = result xor (result shr 11'u32)
+  result = result xor ((7'u32 shl result) and 0x9d2c5680'u32)
+  result = result xor ((15'u32 shl result) and 0xefc60000'u32)
+  result = result xor (result shr 18'u32)
 
 # Test
 when not defined(testing) and isMainModule:
diff --git a/web/news.txt b/web/news.txt
index e818ed66e..82ed4fe44 100644
--- a/web/news.txt
+++ b/web/news.txt
@@ -20,6 +20,9 @@ Changes affecting backwards compatibility
   new experimental ``this`` pragma to achieve a similar effect to what the old ``using`` statement tried to achieve.
 - Typeless parameters have been removed from the language since it would
   clash with ``using``.
+- Procedures in ``mersenne.nim`` (Mersenne Twister implementation) no longer
+  accept and produce ``int`` values which have platform-dependent size -
+  they use ``uint32`` instead.
 
 
 Library Additions