What immediate range does C.ADDI encode?
The CI format combines imm[5] and imm[4:0] into a signed 6-bit immediate, so it represents -32 through 31; regular C.ADDI does not use zero.
C.ADDI
RISC-V C.ADDI Instruction Details
Instruction ManualCI formatRegular C.ADDI adds a nonzero sign-extended 6-bit immediate to a nonzero rd: rd += imm. CI format.
Instruction Syntax
c.addi rd, imm
Operand Breakdown
This is a CI format-format instruction. Confirm operand positions based on the assembly syntax.
CCompressed Instruction
Instruction Behavior
Regular C.ADDI uses the CI format to add a nonzero sign-extended 6-bit immediate to a nonzero rd and write rd; it expands to addi rd, rd, imm. Encodings with nonzero rd and imm=0 are HINTs. rd=x0 with imm=0 is C.NOP; C.NOP encodings with nonzero imm are also HINTs.
C.ADDI Decode And Execute Animation
Decodes the real 16-bit CR or CI encoding and distinguishes normal instructions, HINTs, and shared encodings.
Current Step
Step 1: identify C.ADDI
The animation shows C-extension 16-bit fields directly instead of pretending this is a 32-bit scalar instruction.
C.ADDI Execution Path
read old x10 = 0x0000000Csign-extend 6-bit imm to XLEN = -5write x10 = 0x00000007
This has the same calculation as addi rd, rd, imm; C.ADDI differs only in its 16-bit CI encoding and 6-bit immediate.
16-bit Encoding
0x156D = 0001010101101101funct3 [15..13]
000
imm[5] [12]
1
rd [11..7]
01010
imm[4:0] [6..2]
11011
op [1..0]
01
Operands And Calculation
x10 = 0x0000000C
sext(imm[5:0]) = -5
0x0000000C + -5 (mod 2^32)
Decoded Result And Architectural State
C.ADDI
x10 = 0x00000007
This animation shows only officially defined decode, register reads, arithmetic, and architectural state, not a particular implementation's pipeline, cache, prediction, or timing.
Quick Understanding & Search Notes
C.ADDI is a 16-bit CI encoding for adding a signed 6-bit immediate to rd itself; the regular instruction form excludes rd=x0 and imm=0.
The immediate ranges from -32 to 31 and is sign-extended to XLEN before the addition.
Nonzero rd with imm=0 is a HINT; rd=x0 with imm=0 is C.NOP, so these encodings must not be shown as ordinary C.ADDI arithmetic.
Common Usage Scenarios
Basic Arithmetic
Understand this scenario with real code like «c.addi x10, 5 # x10 += 5».
Loops & Iteration
Understand this scenario with real code like «c.addi x10, 5 # x10 += 5».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is CI format.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
Regular C.ADDI requires nonzero rd and nonzero imm; do not treat the imm=0 HINT as an addition.
rd=x0 with imm=0 is C.NOP, not regular C.ADDI.