Strange branching performance

[David Chase]

On 2014-02-14, at 1:46 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:

> Equality test does not set carry flag. You code is for if (P < Q) { X+1 }

Be careful with the carry flag after cmp -- from the Intel docs:

The condition codes used by the Jcc, CMOVcc, and SETcc instructions are based on the results of a CMP instruction. Appendix B, “EFLAGS Condition Codes,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, shows the relationship of the status flags and the condition codes.

-and-

The terms “above” and “below” are associated with the CF flag and refer to the relation between two unsigned integer values. The terms “greater” and “less” are asso- ciated with the SF and OF flags and refer to the relation between two signed integer values.

David

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