Implement gm_memcmp, your own memcmp, which compares the first n bytes of two memory blocks and returns an integer whose sign reflects which block is larger.

• Walk both blocks one byte at a time, from index 0 up to but not including index n.
• Treat each byte as an unsigned char before comparing: a byte like 0xFF must count as 255, not as a negative number.
• At the first position where the two bytes differ, return the difference of those bytes (first minus second).
• Keep comparing across any \0 bytes inside the blocks, unlike string functions, gm_memcmp never stops early at a null byte; only n bounds the scan.
• Return 0 when all n bytes are equal, and in particular return 0 when n is 0 without reading either pointer.
• Only the sign of the result is meaningful and portable (negative, zero, positive); do not rely on an exact magnitude.

Implement gm_memcmp, your own memcmp, which compares the first n bytes of two memory blocks and returns an integer whose sign reflects which block is larger.

• Walk both blocks one byte at a time, from index 0 up to but not including index n.
• Treat each byte as an unsigned char before comparing: a byte like 0xFF must count as 255, not as a negative number.
• At the first position where the two bytes differ, return the difference of those bytes (first minus second).
• Keep comparing across any \0 bytes inside the blocks, unlike string functions, gm_memcmp never stops early at a null byte; only n bounds the scan.
• Return 0 when all n bytes are equal, and in particular return 0 when n is 0 without reading either pointer.
• Only the sign of the result is meaningful and portable (negative, zero, positive); do not rely on an exact magnitude.