fixes #23915; std/random produces different results on c/js (#24003)

fixes #23915

lib/pure/random.nim

@@ -79,15 +79,28 @@ when defined(nimPreviewSlimSystem):
 
 include system/inclrtl
 {.push debugger: off.}
+template whenHasBigInt64(yes64, no64): untyped =
+  when defined(js):
+    when compiles(compileOption("jsbigint64")):
+      when compileOption("jsbigint64"):
+        yes64
+      else:
+        no64
+    else:
+      no64
+  else:
+    yes64
 
-when defined(js):
-  type Ui = uint32
 
-  const randMax = 4_294_967_295u32
-else:
+whenHasBigInt64:
   type Ui = uint64
 
   const randMax = 18_446_744_073_709_551_615u64
+do:
+  type Ui = uint32
+
+  const randMax = 4_294_967_295u32
+
 
 type
   Rand* = object ## State of a random number generator.
@@ -105,17 +118,17 @@ type
                  ## generator are **not** thread-safe!
     a0, a1: Ui
 
-when defined(js):
-  var state = Rand(
-    a0: 0x69B4C98Cu32,
-    a1: 0xFED1DD30u32) # global for backwards compatibility
-else:
+whenHasBigInt64:
   const DefaultRandSeed = Rand(
     a0: 0x69B4C98CB8530805u64,
     a1: 0xFED1DD3004688D67CAu64)
 
   # racy for multi-threading but good enough for now:
   var state = DefaultRandSeed # global for backwards compatibility
+do:
+  var state = Rand(
+    a0: 0x69B4C98Cu32,
+    a1: 0xFED1DD30u32) # global for backwards compatibility
 
 func isValid(r: Rand): bool {.inline.} =
   ## Check whether state of `r` is valid.
@@ -208,10 +221,10 @@ proc skipRandomNumbers*(s: var Rand) =
     doAssert vals == [501737, 497901, 500683, 500157]
 
 
-  when defined(js):
-    const helper = [0xbeac0467u32, 0xd86b048bu32]
-  else:
+  whenHasBigInt64:
     const helper = [0xbeac0467eba5facbu64, 0xd86b048b86aa9922u64]
+  do:
+    const helper = [0xbeac0467u32, 0xd86b048bu32]
   var
     s0 = Ui 0
     s1 = Ui 0
@@ -294,7 +307,13 @@ proc rand*(r: var Rand; max: range[0.0 .. high(float)]): float {.benign.} =
 
   let x = next(r)
   when defined(js):
-    result = (float(x) / float(high(uint32))) * max
+    when compiles(compileOption("jsbigint64")):
+      when compileOption("jsbigint64"):
+        result = (float(x) / float(high(uint64))) * max
+      else:
+        result = (float(x) / float(high(uint32))) * max
+    else:
+      result = (float(x) / float(high(uint32))) * max
   else:
     let u = (0x3FFu64 shl 52u64) or (x shr 12u64)
     result = (cast[float](u) - 1.0) * max

tests/stdlib/trandom.nim

@@ -47,6 +47,8 @@ block:
   type DiceRoll = range[0..6]
   when not defined(js):
     doAssert rand(DiceRoll).int == 3
+  elif compileOption("jsbigint64"):
+    doAssert rand(DiceRoll).int == 1
   else:
     doAssert rand(DiceRoll).int == 6
 
@@ -296,10 +298,13 @@ block: # bug #22360
     else:
       inc fc
 
-  when defined(js):
-    when compileOption("jsbigint64"):
-      doAssert (tc, fc) == (517, 483), $(tc, fc)
-    else:
-      doAssert (tc, fc) == (515, 485), $(tc, fc)
+  when defined(js) and not compileOption("jsbigint64"):
+    doAssert (tc, fc) == (515, 485), $(tc, fc)
   else:
     doAssert (tc, fc) == (510, 490), $(tc, fc)
+
+block:
+  when defined(js) and not compileOption("jsbigint64"):
+    doAssert rand(int32.high) == 335507522
+  else:
+    doAssert rand(int32.high) == 607539621