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Unified Diff: src/x64/code-stubs-x64.cc

Issue 10939013: Improve the assembly code for power function with integer exponential on x64 (Closed) Base URL: http://v8.googlecode.com/svn/branches/bleeding_edge/
Patch Set: Created 8 years, 3 months ago
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Index: src/x64/code-stubs-x64.cc
===================================================================
--- src/x64/code-stubs-x64.cc (revision 12493)
+++ src/x64/code-stubs-x64.cc (working copy)
@@ -2262,21 +2262,28 @@
__ movsd(double_scratch2, double_result); // Load double_exponent with 1.
// Get absolute value of exponent.
- Label no_neg, while_true, no_multiply;
+ Label no_neg, while_true, while_false;
__ testl(scratch, scratch);
__ j(positive, &no_neg, Label::kNear);
__ negl(scratch);
__ bind(&no_neg);
+ __ j(zero, &while_false, Label::kNear);
+ __ shrl(scratch, Immediate(1));
+ // Above condition means CF=0 && ZF =0.
+ // So the last shifted bit is 0 and the rest is not 0.
+ __ j(above, &while_true, Label::kNear);
+ __ movsd(double_result, double_scratch);
+ __ j(zero, &while_false, Label::kNear);
+
__ bind(&while_true);
__ shrl(scratch, Immediate(1));
- __ j(not_carry, &no_multiply, Label::kNear);
+ __ mulsd(double_scratch, double_scratch);
+ __ j(above, &while_true, Label::kNear);
__ mulsd(double_result, double_scratch);
- __ bind(&no_multiply);
-
- __ mulsd(double_scratch, double_scratch);
__ j(not_zero, &while_true);
+ __ bind(&while_false);
// If the exponent is negative, return 1/result.
__ testl(exponent, exponent);
__ j(greater, &done);
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