Smmul - ST STM32F4 Series Programming Manual

PM0214
SMMLS
3.6.8

SMMUL

Signed most significant word multiply
Syntax
op{R}{cond} Rd, Rn, Rm
Where:
•
op is one of the following:
SMMUL: Signed most significant word multiply.
R: a rounding error flag. If R is specified, the result is rounded instead of being
truncated. In this case the constant 0x80000000 is added to the product before the high
word is extracted.
•
'cond' is an optional condition code (see
• 'Rd' is the destination register.
•
'Rn', 'Rm' are registers holding the first and second operands.
Operation
The SMMUL instruction interprets the values from Rn and Rm as two's complement 32-bit
signed integers. The SMMUL instruction:
1. Multiplies the values from Rn and Rm.
2. Optionally rounds the result, otherwise truncates the result.
3. Writes the most significant signed 32 bits of the result in Rd.
Restrictions
In this instruction: Do not use either SP or PC.
Condition flags
This instruction does not affect the condition code flags.
Examples
SMULL
SMULLR
R4, R5, R3, R8
R0, R4, R5 ; Multiplies R4 and R5, truncates top 32 bits
; and writes to R0
R6, R2 ; Multiplies R6 and R2, rounds the top 32 bits
; and writes to R6.
DocID022708 Rev 6
The STM32 Cortex-M4 instruction set
; Multiplies R5 and R3, extracts top 32 bits,
; subtracts R8, truncates and writes to R4.
Conditional execution on page 64).
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