Texas Instruments TMS320C28x, Reference Manual

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CMPL ACC,P << PM
6-81
CMPL ACC,P << PM Compare 32-bit Value
SYNTAX OPTIONS OPCODE OBJMODE RPT CYC
CMPL ACC,P << PM
1111 1111 0101 1001
X − 1
Operands ACC Accumulator register
P Product register
<<PM Product shift mode
Description The content of the ACC register is compared with the content of the P register,
shifted by the amount specified by the product shift mode (PM). The status
flag bits are set according to the result of (ACC − [ P << PM]). The content of the
ACC register and the P register are left unchanged:
Modify flags on (ACC − [P << PM]);
Flags
and
Modes
N If the result of the operation is negative, then N is set; otherwise it is cleared.
The CMPL instruction assumes infinite precision when it determines the sign
of the result. For example, consider the subtraction 0x8000 0000 − 0x0000
0001. If the precision were limited to 32 bits, the result would cause an
overflow to the positive number 0x7FFF FFFF and N would be cleared.
However, because the CMPL instruction assumes infinite precision, it would
set N to indicate that 0x8000 0000 − 0x0000 0001 actually results in a
negative number.
Z The comparison is tested for a zero condition. The zero flag bit is set if the
operation (AX − [P<<PM]) = 0, otherwise, it is cleared.
C If the subtraction generates a borrow, C is cleared; otherwise C is set.
PM The value in the PM bits sets the shift mode for the output operation from the
product register. If the product shift value is positive (logical left shift
operation), then the low bits are zero filled. If the product shift value is
negative (arithmetic right shift operation), the upper bits are sign extended.
Repeat This instruction is not repeatable. If this instruction follows the RPT
instruction, it resets the repeat counter (RPTC) and executes only once.
Example
; Compare the following (VarA − VarB >> 4):
MOVL ACC,@VarA ; ACC = VarA
SPM −4 ; Set the product shift mode to ”>> 4”
MOVL P,@VarB ; P = VarB
CMPL ACC,P << PM ; Compare (VarA − VarB >> 4)