PM0214 datasheet(118/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

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DocID022708 Rev 4

3.6.7

SMMLA and SMMLS

Signed most significant word multiply accumulate / multiply subtract

Syntax

op{R}{cond} Rd, Rn, Rm, Ra

where:

•

op is one of:

SMMLA: Signed most significant word multiply accumulate.

SMMLS: Signed most significant word multiply subtract.

•

R is a rounding error flag. If R is specified, the result is rounded instead of being

truncated, 0x80000000 is added to the product before the high word is extracted.

•

‘cond’ is an optional condition code (see Conditional execution on page 64)

•

‘Rd’ is the destination register.

•

‘Rn’, ‘Rm’ are registers holding the first and second multiply operands

•

‘Ra’ is the register holding the accumulate value

Operation

The SMMLA instruction interprets the values from Rn and Rm as signed 32-bit words:

Multiplies the values in Rn and Rm.

Optionally rounds the result by adding 0x80000000.

Extracts the most significant 32 bits of the result.

Adds the value of Ra to the signed extracted value.

Writes the result of the addition in Rd.

The SMMLS instruction interprets the values from Rn and Rm as signed 32-bit words:

Multiplies the values in Rn and Rm.

Optionally rounds the result by adding 0x80000000.

Extracts the most significant 32 bits of the result.

Subtracts the extracted value of the result from the value in Ra.

Writes the result of the subtraction in Rd.

Restrictions

In these instructions: Do not use SP or PC.

Condition flags

These instructions do not affect the condition code flags.

Examples

SMMLA

R0, R4, R5, R6

; Multiplies R4 and R5, extracts top 32 bits,

; adds R6, truncates and writes to R0

SMMLAR

R6, R2, R1, R4

; Multiplies R2 and R1, extracts top 32 bits,

; adds R4, rounds and writes to R6

SMMLSR

R3, R6, R2, R7

; Multiplies R6 and R2, extracts top 32 bits,

; subtracts R7, rounds and writes to R3

SMMLS

R4, R5, R3, R8

; Multiplies R5 and R3, extracts top 32 bits,

; subtracts R8, truncates and writes to R4.

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