Saturating Instructions; Table 29. Saturating Instructions - ST STM32F4 Series Programming Manual

The STM32 Cortex-M4 instruction set
3.7

Saturating instructions

This section describes the saturating instructions.
Mnemonic
SSAT Signed Saturate
SSAT16 Signed Saturate Halfword
USAT Unsigned Saturate
USAT16 Unsigned Saturate Halfword
QADD Saturating Add
QSUB Saturating Subtract
QSUB16 Saturating Subtract 16
QASX Saturating Add and Subtract with Exchange
QSAX Saturating Subtract and Add with Exchange
QDADD Saturating Double and Add
QDSUB Saturating Double and Subtract
UQADD16 Unsigned Saturating Add 16
UQADD8 Unsigned Saturating Add 8
UQASX Unsigned Saturating Add and Subtract with Exchange
UQSAX Unsigned Saturating Subtract and Add with Exchange
UQSUB16 Unsigned Saturating Subtract 16
UQSUB8 Unsigned Saturating Subtract 8
For signed n-bit saturation, this means that:
•
if the value to be saturated is less than -2
•
if the value to be saturated is greater than 2
•
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 2
•
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
page 186.
To read the state of the Q flag, use the MRS instruction, see
124/260

Table 29. Saturating instructions

Brief description
DocID022708 Rev 6
SSAT and USAT on page 125
SSAT16 and USAT16 on page 126
SSAT and USAT on page 125
SSAT16 and USAT16 on page 126
QADD and QSUB on page 127
QADD and QSUB on page 127
QADD and QSUB on page 127
QASX and QSAX on page 128
QASX and QSAX on page 128
QDADD and QDSUB on page 129
QDADD and QDSUB on page 129
UQADD and UQSUB on page 131
UQADD and UQSUB on page 131
UQASX and UQSAX on page 130
UQASX and UQSAX on page 130
UQADD and UQSUB on page 131
UQADD and UQSUB on page 131
n-1
, the result returned is -2
n-1
-1, the result returned is 2
n-1
, the result returned is 2
MRS on page
PM0214
See
n-1
n-1
-1
n-1
MSR on
185.