Author: Dezhi Zhao
Date: 03:37:38 06/12/98
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On June 12, 1998 at 03:41:43, Vincent Diepeveen wrote: >Now what's more likely: BSF/R to become faster in future or mispredicted >branches becoming faster :) Yes. It only takes 1 or 2 cycles on PII if the 2 operands are both in registers. However there some problems with BSF/R instructions. 1. They are machine dependent. 2. There are no (BSF/R) operators in C or C++ compliers. You have to use them as asm inline. eg: int bit_string; int index_first1; _asm index_first1, bit_string After you disassembly the above, you will find the compiler generated code is far from optimal. Compiler will treat index_first1 and bit_string as memory operands, and reload them each time it encounter them. The memory reloads also harms the optimization of the inline c/c++ neighbor codes.
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