x86add.b
LBT intrinsic · group: x86 Integer
Synopsis
Instruction: x86add.b rj, rk
CPU Flags: LBT
Description
x86-style add: add 8-bit values in rj and rk. Update EFLAGS (CF, AF, OF, PF, ZF, SF) according to the result. Only EFLAGS (LBT4) is updated; the GPR is not modified.
Operation
uint8_t lhs = (uint8_t)a;
uint8_t rhs = (uint8_t)b;
uint8_t result = lhs + rhs;
EFLAGS.CF = (uint64_t)lhs + (uint64_t)rhs > UINT8_MAX;
EFLAGS.AF = ((lhs ^ rhs ^ result) & 0x10) != 0;
EFLAGS.OF = ((~(lhs ^ rhs)) & (lhs ^ result) & 0x80) != 0;
EFLAGS.PF = parity_even((uint8_t)result);
EFLAGS.ZF = result == 0;
EFLAGS.SF = (int8_t)result < 0;
Tested on real machine.
Latency and Throughput
| CPU | µarch | Latency | Throughput (IPC) |
|---|---|---|---|
| 3C5000 | LA464 | 2 | 0.5(1/2) |
| 3C6000 | LA664 | 2 | 0.5(1/2) |