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139
SAM4CP [DATASHEET]
43051E–ATPL–08/14
12.6.7.1 SSAT and USAT
Signed Saturate and Unsigned Saturate to any bit position, with optional shift before saturating.
Syntax
op
{
cond
}
Rd
, #
n
,
Rm
{,
shift
#s}
where:
op
is one of:
SSAT Saturates a signed value to a signed range.
USAT Saturates a signed value to an unsigned range.
cond
is an optional condition code, see
“Conditional Execution”
.
Rd
is the destination register.
n
specifies the bit position to saturate to:
n ranges from 1
n ranges from 0 to 31 for USAT.
to 32 for SSAT
Rm
is the register containing the value to saturate.
shift #s
is an optional shift applied to Rm before saturating. It must be one of the following:
ASR #s
where s is in the range 1 to 31.
LSL #s
where
s
is in the range 0 to 31.
Operation
These instructions saturate to a signed or unsigned
n
-bit value.
The SSAT instruction applies the specified shift, then saturates to the signed range -2
n
–1
≤
x
≤
2
n
–1
-1.
The USAT instruction applies the specified shift, then saturates to the unsigned range 0
≤
x
≤
2
n
-1.
Restrictions
Do not use SP and do not use PC
.
Condition Flags
These instructions do not affect the condition code flags.
If saturation occurs, these instructions set the Q flag to 1.
Examples
SSAT R7, #16, R7, LSL #4 ; Logical shift left value in R7 by 4, then
; saturate it as a signed 16-bit value and
; write it back to R7
USATNE R0, #7, R5 ; Conditionally saturate value in R5 as an
; unsigned 7 bit value and write it to R0.