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add with carry

An add that also adds in the carry flag from the previous add, so big numbers can be added in 64-bit pieces.

adc (x86-64; ARM64 adc/adcs) computes a + b + C; chained after an add of the low halves it propagates the carry into the high halves. RISC-V has no carry flag and recovers the carry with sltu.

Examples

  • Adding two 128-bit numbers on x86-64: add rax, rcx for the low halves, then adc rdx, rbx for the high halves plus the carry.

See also

carry flag carry
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