PM0214 datasheet(124/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

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3.7

Saturating instructions

This section describes the saturating instructions.

For signed n-bit saturation, this means that:

•

if the value to be saturated is less than -2n-1, the result returned is -2n-1

•

if the value to be saturated is greater than 2n-1-1, the result returned is 2n-1-1

•

otherwise, the result returned is the same as the value to be saturated.

For unsigned n-bit saturation, this means that:

•

if the value to be saturated is less than 0, the result returned is 0

•

if the value to be saturated is greater than 2n-1, the result returned is 2n-1

•

otherwise, the result returned is the same as the value to be saturated.

If the returned result is different from the value to be saturated, it is called saturation. If

saturation occurs, the instruction sets the Q flag to 1 in the APSR. Otherwise, it leaves the Q

flag unchanged. To clear the Q flag to 0, you must use the MSR instruction, see MSR on

page 174.

To read the state of the Q flag, use the MRS instruction, see MRS on page 173.

Table 30. Saturating instructions

Mnemonic

Brief description

See

SSAT

Signed Saturate

SSAT and USAT on page 125

SSAT16

Signed Saturate Halfword

SSAT16 and USAT16 on page 126

USAT

Unsigned Saturate

SSAT and USAT on page 125

USAT16

Unsigned Saturate Halfword

SSAT16 and USAT16 on page 126

QADD

Saturating Add

QADD and QSUB on page 127

QSUB

Saturating Subtract

QADD and QSUB on page 127

QSUB16

Saturating Subtract 16

QADD and QSUB on page 127

QASX

Saturating Add and Subtract with Exchange

QASX and QSAX on page 128

QSAX

Saturating Subtract and Add with Exchange

QASX and QSAX on page 128

QDADD

Saturating Double and Add

QDADD and QDSUB on page 129

QDSUB

Saturating Double and Subtract

QDADD and QDSUB on page 129

UQADD16

Unsigned Saturating Add 16

UQADD and UQSUB on page 131

UQADD8

Unsigned Saturating Add 8

UQADD and UQSUB on page 131

UQASX

Unsigned Saturating Add and Subtract with Exchange

UQASX and UQSAX on page 130

UQSAX

Unsigned Saturating Subtract and Add with Exchange

UQASX and UQSAX on page 130

UQSUB16

Unsigned Saturating Subtract 16

UQADD and UQSUB on page 131

UQSUB8

Unsigned Saturating Subtract 8

UQADD and UQSUB on page 131

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