s_flbit_i32 GPU Native ISA AMD Scalar

S FLBIT I32 Scalar Arithmetic

s_flbit_i32

Count the number of leading bits that are the same as the sign bit of a scalar input and store the result into a scalar register.

Encoding

Verified bit-level encoding data is not yet available for this instruction. The instruction-format classification below (SOP1) is well-documented and stable; exact per-target opcode/field bit positions have not yet been imported from a verified source.
Format SOP1
Execution Unit

Operands

Operand details have not yet been curated for this instruction.

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related PTX Concepts

Count Leading Zeros ↗
equivalent with restrictions
clz (PTX)

Related

More in Scalar Arithmetic

Reference

AMDGPU / GFX ISA

Description

Count the number of leading bits that are the same as the sign bit of a scalar input and store the result into a scalar register. Store -1 if all input bits are the same.

Semantics

tmp = -1; // Set if all bits are the same for i in 1 : 31 do // Search from MSB if S0.u32[31 - i] != S0.u32[31] then tmp = i; break endif endfor; D0.i32 = tmp

Example

S_FLBIT_I32(0x00000000) => 0xffffffff
S_FLBIT_I32(0x0000cccc) => 16
S_FLBIT_I32(0xffff3333) => 16
S_FLBIT_I32(0x7fffffff) => 1

Reproduced from AMD's official "AMD Instinct MI300" ISA Reference Guide for technical accuracy.

Sources