Slide 15.6: IDIV instruction

IDIV Instruction

The IDIV (signed divide) instruction performs signed integer division, using the same operands as the DIV instruction.

IDIV — Signed Integer Division

Usage: idiv src

Flag	O	D	I	S	Z	A	P	C
Result	?			?	?	?	?	?

Signed binary division of accumulator by source. If source is a byte value, AX is divided by “src” and the quotient is stored in AL and the remainder in AH. If source is a word value, DX:AX is divided by “src”, and the quotient is stored in AL and the remainder in DX.

	Clocks
Operands	286	386	486	Size Bytes
reg8	17	19	19	2
reg16	25	27	27	2
reg32		43	43	2
mem8	22	22	20	2-4
mem16	38	30	28	2-4
mem32		46	44	2-4

If the divisor equals zero, jump past division instruction.
A divide overflow condition results if a quotient is too large to fit into the destination. This causes a CPU interrupt and program halted.

8-Bit Signed Division	Divided by Zero	Divide Overflow
.data x SWORD 2001h y SBYTE 80h .code movsx eax, x idiv y call WriteHex	.data x SWORD -101h y SBYTE 10h .code mov eax, 0 mov ax, x test y, 0FFh jz ABORT idiv y call WriteHex ABORT: exit	.data x SWORD -1010h y SBYTE 10h .code mov eax, 0 mov ax, x idiv y call WriteHex
Output	Output	Output
AL = AH =	AL = AH =	AL = AH =