Texas Instruments TMS320C28x, Reference Manual, Page: 240 / 695

CSB ACC
6-83
CSB ACC Count Sign Bits
SYNTAX OPTIONS OPCODE OBJMODE RPT CYC
CSB ACC
0101 0110 0011 0101
1 − 1
Operands ACC Accumulator register
Description
Count the sign bits in the ACC register by determining the number of leading 0s
or 1s in the ACC register and storing the result, minus one, in the T register:
T = 0, 1 sign bit
T = 1, 2 sign bits
.
.
T = 31, 32 sign bits
Note: The count sign bit operation is often used in normalization operations and is particularly
useful for algorithms such as; calculating Square Root of a number, calculating the
inverse of a number, searching for the first ”1” bit in a word.
Flags and
Modes
N N is set if bit 31 of ACC is 1, else N is cleared.
Z Z is set if ACC is 0, else Z is cleared.
TC
The TC bit will reflect the state of the sign bit after the operation (TC=1 for
negative).
Repeat This instruction is not repeatable. If this instruction follows the RPT
instruction, it resets the repeat counter (RPTC) and executes only once.
Example
; Normalize the contents of VarA:
MOVL ACC,@VarA ; Load ACC with contents of VarA
CSB ACC ; Count sign bits
LSLL ACC,T ; Logical shift left ACC by T(4:0)
MOVL @VarA,ACC ; Store result into VarA