The code is compiled as it is in order to handle the case where the indexes need to wrap around. Suppose i1=0xffffffff on entry - you then want to access block[

The code is compiled as it is in order to handle the case where the indexes need to wrap around. Suppose i1=0xffffffff on entry - you then want to access block[0x00000000ffffffff], block[0x0000000000000000], block[0x00000000000000001]. I've written out all 64 bits of the offset, in the hope this makes the problem clearer: there's no addressing mode for getting the 32 bit truncation. That's why there's an LEAs after each access. (Note that they write to the 32 bit part of each register.) In the int32_t case, suppose i1=-1. Then you want to access block[0xffffffffffffffff], block[0x0000000000000000], block[0x0000000000000001], and so on. You can do an initial sign extension of the indexes, and then the base64+index64+disp32 addressing mode gives you the right result. Make the unsigned version take uint64_t indices, and you get the same code for both. Or #include <stddef.h>, and make it take size_t - same thing. This is exactly the sort of thing that size_t is there for.