Texas Instruments TMS320C67X/C67X+ DSP Subtract Conditionally and Shift-Used for Division, Subc

SUBC Subtract Conditionally and Shift−Used for Division

				Subtract Conditionally and Shift—Used for Division
SUBC
Syntax					SUBC (.unit) src1, src2, dst
					.unit = .L1 or .L2
Compatibility					C62x, C64x, C67x, and C67x+ CPU
Opcode
31	29	28	27	23		22	18	17	13	12	11	5	4	3	2	1	0

creg

z

dst

src2

src1

x

1 0 0 1 0 1 1 1 1 0 s p

3	1	5	5	5	1	1	1
			Opcode map field used...	For operand type...		Unit
			src1	uint		.L1, .L2
			src2	xuint
			dst	uint

Description

Execution

Pipeline

Subtract src2 from src1. If result is greater than or equal to 0, left shift result by 1, add 1 to it, and place it in dst. If result is less than 0, left shift src1 by 1, and place it in dst. This step is commonly used in division.

if (cond)	{
	if (src1 − src2 w 0)
	( (src1−src2) << 1) + 1 → dst
	else src1 << 1 → dst
	}
else nop
Pipeline	E1
Stage
Read	src1, src2
Written	dst
Unit in use	.L

Instruction Type	Single-cycle
Delay Slots	0
See Also	ADD, SSUB, SUB, SUBDP, SUBSP, SUBU, SUB2

3-258 Instruction Set SPRU733