1 files changed, 39 insertions, 0 deletions
diff --git a/lib/system/bitmasks.nim b/lib/system/bitmasks.nim
new file mode 100644
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+++ b/lib/system/bitmasks.nim
@@ -0,0 +1,39 @@
+#
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2015 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+# Page size of the system; in most cases 4096 bytes. For exotic OS or
+# CPU this needs to be changed:
+const
+  PageShift = when defined(nimPage256) or defined(cpu16): 3
+              elif defined(nimPage512): 9
+              elif defined(nimPage1k): 10
+              else: 12 # \ # my tests showed no improvements for using larger page sizes.
+
+  PageSize = 1 shl PageShift
+  PageMask = PageSize-1
+
+
+  MemAlign = # also minimal allocatable memory block
+    when defined(nimMemAlignTiny): 4
+    elif defined(useMalloc):
+      when defined(amd64): 16 
+      else: 8
+    else: 16
+
+  BitsPerPage = PageSize div MemAlign
+  UnitsPerPage = BitsPerPage div (sizeof(int)*8)
+    # how many ints do we need to describe a page:
+    # on 32 bit systems this is only 16 (!)
+
+  TrunkShift = 9
+  BitsPerTrunk = 1 shl TrunkShift # needs to be power of 2 and divisible by 64
+  TrunkMask = BitsPerTrunk - 1
+  IntsPerTrunk = BitsPerTrunk div (sizeof(int)*8)
+  IntShift = 5 + ord(sizeof(int) == 8) # 5 or 6, depending on int width
+  IntMask = 1 shl IntShift - 1