[project @ 1996-01-08 20:28:12 by partain]

[ghc-hetmet.git] / ghc / docs / NOTES.arbitary-ints

diff --git a/ghc/docs/NOTES.arbitary-ints b/ghc/docs/NOTES.arbitary-ints
new file mode 100644 (file)
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+++ b/ghc/docs/NOTES.arbitary-ints
@@ -0,0 +1,54 @@
+
+Boxed structure of BigInts
+
+
+---->  Info1   Pointer
+               |               Pointer passed to BigNum package
+               |               |
+               \/              \/
+               Info2   Size    Integer ....
+
+                       (size excludes info ptr & size field)
+
+Unboxed (Compiler must place on pointer stack not data stack
+        Must also tell GC if it is in a register when GC invoked)
+
+---->  Info2   Size    Integer
+
+
+
+Info1:
+       SPEC_INFO_TABLE(Info1, BigNum_entry, 1, 1);     (Min Size 2 ?)
+
+       Entering this returns the BigNum using agreed return convention
+
+Info2:
+       DATA_INFO_TABLE(Info2, Dummy_entry);
+
+       This never actually entered -- just required for GC.
+
+------------------------------------------------------------------------------
+
+Boxed structure of BigInts (the alternative one)
+
+                       Pointer passed to BigNum package
+                       |
+                       \/
+---->  Info    Size    Integer ....
+
+               (size excludes info ptr & size field)
+
+Unboxed (Compiler must place on pointer stack not data stack
+        Must also tell GC if it is in a register when GC invoked)
+
+
+Info:
+       DATA_INFO_TABLE(Info, BigNum_entry);
+
+       Entering this returns the BigNum using agreed return convention
+
+
+
+Note that the Boxed and Unboxed representation are identical !!!
+
+(unboxing represents evaluationhood, not pointerhood)