Instruction Syntax
| Mnemonic | Format | Flags |
| divw | rD,rA,rB | OE = 0, Rc = 0 |
| divw. | rD,rA,rB | OE = 0, Rc = 1 |
| divwo | rD,rA,rB | OE = 1, Rc = 0 |
| divwo. | rD,rA,rB | OE = 1, Rc = 1 |
Instruction Encoding
| Field | Bits | Description |
| Primary Opcode | 0-5 | 011111 (0x1F) |
| rD | 6-10 | Destination register |
| rA | 11-15 | Dividend register |
| rB | 16-20 | Divisor register |
| OE | 21 | Overflow Exception |
| XO | 22-30 | 111101011 (491) |
| Rc | 31 | Record Condition Register |
Operation
rD ← (rA) ÷ (rB)
The signed contents of register rA are divided by the signed contents of register rB. The signed quotient is placed in register rD. Both operands and the result are interpreted as 32-bit signed integers.
Note: Division by zero and overflow conditions are handled according to the OE bit setting. If the quotient cannot be represented in 32 bits, the result is undefined.
Affected Registers
Condition Register (CR0 field)
(if Rc = 1)
- LT (Less Than)
- GT (Greater Than)
- EQ (Equal)
- SO (Summary Overflow)
Note: CR0 field may not reflect the correct comparison if overflow occurs (see XER below).
XER (Exception Register)
(if OE = 1)
- SO (Summary Overflow)
- OV (Overflow)
Overflow occurs when:
For more information on condition codes see Section 2.1.3, "Condition Register," and Section 2.1.5, "XER Register," in the PowerPC Microprocessor Family: The Programming Environments manual.
Examples
Basic Division
li r4, 100 # Dividend = 100 li r5, 4 # Divisor = 4 divw r3, r4, r5 # r3 = 100 / 4 = 25
Signed Division
li r4, -100 # Dividend = -100 li r5, 3 # Divisor = 3 divw r3, r4, r5 # r3 = -100 / 3 = -33 (truncated toward zero)
Division with Condition Register
li r4, 50 # Dividend li r5, 7 # Divisor divw. r3, r4, r5 # r3 = 50 / 7 = 7, sets CR0 # CR0[LT] = 0, CR0[GT] = 1, CR0[EQ] = 0
Division with Overflow Detection
li r4, 100 # Dividend li r5, 0 # Divisor = 0 (will cause overflow) divwo r3, r4, r5 # Division by zero, sets XER[OV] and XER[SO] # Result is undefined, overflow exception may occur
Safe Division with Check
# Safe division that checks for zero divisor lwz r4, dividend # Load dividend lwz r5, divisor # Load divisor cmpwi r5, 0 # Check if divisor is zero beq div_by_zero # Branch if zero divw r3, r4, r5 # Perform division b div_done # Skip error handling div_by_zero: li r3, 0 # Set result to 0 for zero division # Or handle error as appropriate div_done: # Continue with result in r3
Integer Division with Remainder
# Calculate both quotient and remainder li r4, 17 # Dividend = 17 li r5, 5 # Divisor = 5 divw r3, r4, r5 # r3 = quotient = 3 mullw r6, r3, r5 # r6 = quotient * divisor = 15 subf r7, r6, r4 # r7 = remainder = 17 - 15 = 2