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 146

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

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

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.

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

-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.