x86rotri.b

LBT intrinsic · group: x86 Shift

Synopsis

Instruction: x86rotri.b rj, imm
CPU Flags: LBT

Description

x86-style rotate right: rotate 8-bit value in rj right by immediate imm. Update CF, OF (for shift count of 1). Only EFLAGS (LBT4) is updated; the GPR is not modified.

Operation

uint8_t v = (uint8_t)a;
unsigned c = (unsigned)imm;
unsigned n = c % 8;
uint8_t r = (uint8_t)((v >> n) | (v << (8 - n)));
EFLAGS.CF = ((v >> ((n - 1 + 8) % 8)) & 1);
if (c == 1) {
  EFLAGS.OF = (((v ^ r) & 0x80) != 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)

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