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Unified Diff: src/utils.h

Issue 10197010: Optimise Math.floor(x/y) to use integer division for specific divisor. (Closed) Base URL: http://v8.googlecode.com/svn/branches/bleeding_edge/
Patch Set: Created 8 years, 8 months ago
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Index: src/utils.h
===================================================================
--- src/utils.h (revision 11426)
+++ src/utils.h (working copy)
@@ -85,6 +85,32 @@
}
+// Magic numbers for integer division.
+// These are kind of 2's complement reciprocal of the divisors.
+// Details and proofs can be found in:
+// - Hacker's Delight, Henry S. Warren, Jr.
+// - The PowerPC Compiler Writer’s Guide
+// and probably many others.
+// See details in the implementation of the algorithm in
+// lithium-codegen-arm.cc : LCodeGen::TryEmitSignedIntegerDivisionByConstant().
+struct DivMagicNumbers {
+ unsigned M;
+ unsigned s;
+};
+
+const DivMagicNumbers InvalidDivMagicNumber= {0, 0};
+const DivMagicNumbers DivMagicNumberFor3 = {0x55555556, 0};
+const DivMagicNumbers DivMagicNumberFor5 = {0x66666667, 1};
+const DivMagicNumbers DivMagicNumberFor7 = {0x92492493, 2};
+const DivMagicNumbers DivMagicNumberFor9 = {0x38e38e39, 1};
+const DivMagicNumbers DivMagicNumberFor11 = {0x2e8ba2e9, 1};
+const DivMagicNumbers DivMagicNumberFor25 = {0x51eb851f, 3};
+const DivMagicNumbers DivMagicNumberFor125 = {0x10624dd3, 3};
+const DivMagicNumbers DivMagicNumberFor625 = {0x68db8bad, 8};
+
+const DivMagicNumbers DivMagicNumberFor(int32_t divisor);
+
+
// The C++ standard leaves the semantics of '>>' undefined for
// negative signed operands. Most implementations do the right thing,
// though.
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