4.6. Other ALU Instructions
The principal arithmetic and logical instructions of the Itanium ISA operate on full 64-bit quantities. We have seen, however, that load and store instructions can access smaller information units.
When data are stored, only the lowest-order 1, 2, 4, or 8 bytes in the source register are copied to the destination in memory; the highest 7, 6, 4, or 0 bytes are discarded. For example, the number –2 would be truncated from 0xfffffffffffffffe (64-bit two's complement) to 0xfe (8-bit two's complement) by an st1 instruction. If overflow has already occurred with respect to the destination size, the result stored into memory will be misleading. For example, the number –25710 is truncated from 0xfffffffffffffeff to 0xff (which ...
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