Writing string.h functions using string instructions in asm x86-64 (2025)

Article

• Implements C string.h functions using native x86-64 string instructions.
• Covers SCAS, MOVS, CMPS, LODS, and STOS instruction families.
• Shows how SSE/AVX variants like pcmpestri accelerate string operations.
• Educational deep-dive into hand-optimized low-level string handling.

Discussion

• One commenter questions how to correctly interpret pcmpestri flags vs. ZF/SF after the instruction.

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