armrotr.w
LBT intrinsic · group: ARM Shift
Synopsis
Instruction: armrotr.w rj, rk, cond
CPU Flags: LBT
Description
ARM-style rotate right (32-bit): conditionally rotate value in rj right by amount in rk (masked to 8 bits, rotate modulo 32). Update ARMFLAGS (C, N, Z). Only ARMFLAGS (LBT4) is updated; the GPR is not modified.
Operation
if (arm_cond_holds(ARMFLAGS, cond)) {
uint32_t lhs = (uint32_t)a;
uint32_t rhs = (uint32_t)b;
uint32_t raw_count = rhs & 0xff;
uint32_t c = rhs & 0x1f;
unsigned n = c % 32;
uint32_t r = n == 0 ? lhs : (lhs >> n) | (lhs << (32 - n));
if (raw_count != 0) {
ARMFLAGS.C = n == 0 ? ((lhs >> 31) & 1) : ((lhs >> (n - 1)) & 1);
}
ARMFLAGS.N = (r >> 31) & 1;
ARMFLAGS.Z = r == 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) |