Is the '

Is Comparison '<' Faster than '<='?

In certain scenarios involving complex loop code, it's been suggested that the '<' operator may be faster than the '<=' operator. To investigate this claim, let's examine the underlying machine code generated for these comparisons.

Code Generation

On x86 architectures, integral comparisons are typically implemented using two machine instructions:

1. A test or cmp instruction: This sets the EFLAGS register with various status bits indicating the outcome of the comparison.
2. A jcc (jump) instruction: This checks the EFLAGS and branches accordingly.

For both '<' and '<=' comparisons, the first instruction (a cmp) is identical. The difference lies in the second instruction:

• '<': jge, jump if greater than or equal
• '<=': jg, jump if greater

Execution Time

Execution time is determined by both latency and throughput. In the case of jge and jg instructions, they have the same latency of zero cycles and a throughput of 0.5 cycles. This means they will take the same amount of time to execute.

Floating Point Comparisons

The same principles apply to x87 floating point comparisons using the fucomip instruction. The seta and setae instructions used to check the EFLAGS register also take the same time to execute.

Conclusion

On most architectures, the '<' and '<=' operators have identical execution times for both integral and floating point comparisons. The assumption that '<' might be faster is incorrect in the general case.

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