Does UNZIP access memory?
No. It only rearranges bit fields in integer registers.
UNZIP
RISC-V UNZIP Instruction Details
Instruction ManualI-typeRV32 bit deinterleave (Zbkb), RV32-only.
Instruction Syntax
unzip rd, rs1
RV32 Zbkb 1.0 only; syntax unzip rd, rs1, both integer registers, with no assembly immediate.
32-bit I-type: bits31:20=000010001111, funct3=101, opcode=0010011; the fixed selector is not an arithmetic immediate.
For i=0..15, rd[i]=rs1[2*i] and rd[i+16]=rs1[2*i+1]; inverse of ZIP, with no memory access.
Read the source before writeback; rd=rs1 uses the old source, x0 sources are zero, and rd=x0 discards writeback.
ZbkbBit Manipulation
Instruction Behavior
UNZIP (Zbkb, RV32-only) gathers even-numbered bits of rs1 into the low 16 bits of rd and odd-numbered bits into the high 16 bits: for i=0..15, rd[i]=rs1[2*i] and rd[i+16]=rs1[2*i+1]. It is the inverse of ZIP.
UNZIP Decode & Execute Animation
Shows only specification-defined encodings, conditions, and architectural state.
unzip a0, a1
unzip,
Execution Context
Assumes RV32 Zbkb is implemented. Inputs are unsigned 32-bit patterns; teaching steps are not processor cycles.
Instruction Encoding
31..20
imm[11:0]
000010001111
19..15
rs1
01011
14..12
funct3
101
11..7
rd
01010
6..0
opcode
0010011 OP-IMM
Decode fixed fields
x[a1]=0xD2C4B8A1
rd[i] = rs1[2*i], rd[i+16] = rs1[2*i+1], i=0..15
Architectural state has not been committed.
Quick Understanding & Search Notes
UNZIP gathers even bits of a 32-bit source into the low 16 bits and odd bits into the high 16 bits.
The official encoding and semantics are RV32-only.
It rearranges even source bits into the low half and odd source bits into the high half without accessing memory.
Common Usage Scenarios
Bit deinterleaving
Assume RV32 Zbkb and a1=0xD2C4B8A1; unzip a0, a1 gives a0=0x98ECCA41, leaving the source and memory unchanged.
RV32 SHA3 bit-interleaved representation
Assume RV32 Zbkb and a1=0xD2C4B8A1; unzip a0, a1 gives a0=0x98ECCA41, leaving the source and memory unchanged.
Pre-Use Checklist
Syntax Check
- RV32 Zbkb 1.0 only; syntax unzip rd, rs1, both integer registers, with no assembly immediate.
- 32-bit I-type: bits31:20=000010001111, funct3=101, opcode=0010011; the fixed selector is not an arithmetic immediate.
Semantic Check
- For i=0..15, rd[i]=rs1[2*i] and rd[i+16]=rs1[2*i+1]; inverse of ZIP, with no memory access.
- Read the source before writeback; rd=rs1 uses the old source, x0 sources are zero, and rd=x0 discards writeback.
Pitfalls / Common Confusions
UNZIP is defined only on RV32; there is no RV64 form.
It deinterleaves bits, not bytes or halfwords.
FAQ
Which extension contains UNZIP?
It belongs to the Zbkb cryptographic bit-manipulation extension.