bfi GPU Virtual ISA NVIDIA

bfi Integer Arithmetic Instructions

bfi.type f, a, b, c, d;

Align and insert a bit field from a into b, and place the result in f.

Encoding

PTX is a virtual instruction set. It has no single, stable native binary encoding - the compiler lowers this instruction to different native machine code depending on the selected NVIDIA target architecture (compute capability). This page intentionally shows no bit-diagram; see the target/version requirements below for what governs how this instruction compiles.
PTX ISA Version Introduced PTX ISA 2.0
Minimum Target sm_20

Syntax Forms

One mnemonic covers many type / state-space / scope / modifier combinations - each row below is an independently valid form.

Syntax Data Types State Space(s) Modifiers Min. Target Description
bfi.type f, a, b, c, d; sm_20 Align and insert a bit field from a into b, and place the result in f. Source c gives the starting bit position for the insertion, and source d gives the bit field length in bits. (see the official PTX ISA docs for the full description)

Operands

  • f
    Operand
  • a
    Source operand
  • b
    Source operand
  • c
    Source operand
  • d
    Destination register

At a Glance

Data Types -

Related AMDGPU Concepts

Bit-Field Insert ↗
equivalent with restrictions
v_bfi_b32 (AMDGPU)

Related

More in Integer Arithmetic Instructions

Reference

NVIDIA PTX ISA

Description

Align and insert a bit field from a into b, and place the result in f. Source c gives the starting bit position for the insertion, and source d gives the bit field length in bits. Operands a, b, and f have the same type as the instruction type. Operands c and d are type.u32, but are restricted to the 8-bit value range 0..255. If the bit field length is zero, the result is b. If the start position is beyond the msb of the input, the result is b.

Semantics

msb = (.type==.b32) ? 31 : 63; pos = c & 0xff; // pos restricted to 0..255 range len = d & 0xff; // len restricted to 0..255 range f = b; for (i=0; i<len && pos+i<=msb; i++) { f[pos+i] = a[i]; }

Examples

bfi.b32  d,a,b,start,len;

Reproduced from NVIDIA's official PTX ISA documentation for technical accuracy.

Sources