uhsub8

Unsigned Halving Subtract 8

UHSUB8<c> <Rd>, <Rn>, <Rm>

Unsigned halving subtract of 4 bytes.

Details

Performs unsigned halving subtraction of four 8-bit bytes in parallel. Each byte of Rm is subtracted from the corresponding byte of Rn and the result is divided by 2 (rounded down). No condition flags are affected.

Pseudocode Operation

for i = 0 to 3 do
  byte_rn ← Rn[8*i+7:8*i]; byte_rm ← Rm[8*i+7:8*i]
  diff ← byte_rn - byte_rm
  Rd[8*i+7:8*i] ← diff >> 1

Example

UHSUB8 r0, r1, r2

Encoding

Binary Layout
cond
01100
111
Rn
Rd
1
1
1
1
1
11
1
Rm
 
Format SIMD Integer
Opcode 0x06700FF0
Extension A32 (DSP)

Operands

  • Rd
    Destination general-purpose register
  • Rn
    First source / base general-purpose register
  • Rm
    Second source / offset general-purpose register

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x06700FF0 UHSUB8{<c>}{<q>} {<Rd>,} <Rn>, <Rm> A32 cond | 01100 | 111 | Rn | Rd | 1 | 1 | 1 | 1 | 1 | 11 | 1 | Rm
0xFAC0F060 UHSUB8{<c>}{<q>} {<Rd>,} <Rn>, <Rm> T32 111110101 | 100 | Rn | 1111 | Rd | 0 | 1 | 1 | 0 | Rm

Description

Unsigned Halving Subtract 8 performs four unsigned 8-bit integer subtractions, halves the results, and writes the results to the destination register.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    diff1 = UInt(R[n]<7:0>) - UInt(R[m]<7:0>);
    diff2 = UInt(R[n]<15:8>) - UInt(R[m]<15:8>);
    diff3 = UInt(R[n]<23:16>) - UInt(R[m]<23:16>);
    diff4 = UInt(R[n]<31:24>) - UInt(R[m]<31:24>);
    R[d]<7:0>   = diff1<8:1>;
    R[d]<15:8>  = diff2<8:1>;
    R[d]<23:16> = diff3<8:1>;
    R[d]<31:24> = diff4<8:1>;