Smul And Smulw - ST STM32F4 Series Programming Manual

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3.6.10

SMUL and SMULW

Signed Multiply (halfwords) and Signed Multiply (word by halfword)
Syntax
op{XY}{cond} Rd, Rn, Rm
op{Y}{cond} Rd. Rn, Rm
•
op is one of:
SMUL{XY} Signed multiply (halfwords). X and Y specify which halfword of the source
registers Rn and Rm is used as the first and second multiply operand.
SMULW{Y} Signed multiply (word by halfword). Y specifies which halfword of the
source Rm register is used as the second multiply operand.
•
'cond' is an optional condition code (see
•
'Rd' is the destination register.
•
'Rn', 'Rm' are registers holding the first and second operands
Operation
The SMULBB, SMULTB, SMULBT and SMULTT instructions interprets the values from Rn
and Rm as four signed 16-bit integers. These instructions:
1. Multiply the specified signed halfword, top or bottom, values from Rn and Rm.
2. Write the 32-bit result of the multiplication in Rd.
The SMULWT and SMULWB instructions interprets the values from Rn as a 32-bit signed
integer and Rm as two halfword 16-bit signed integers. These instructions:
1. Multiply the first operand and the top, T suffix, or the bottom, B suffix, halfword of the
second operand.
2. Write the 32 signed most significant bits of the 48-bit result in the destination register.
Restrictions
Do not use either SP or PC.
Examples
SMULBT
R3, R6, R2 ; Multiplies bottom halfword of R4 with bottom halfword
; of R6, subtracts multiplication of top halfword of R6
; with top halfword of R3, writes to R3
R4, R5, R3 ; Multiplies bottom halfword of R5 with top halfword of
; R3, subtracts multiplication of top halfword of R5
; with bottom halfword of R3, writes to R4.
If X is B, then the bottom halfword, bits [15:0] of Rn is used.
If X is T, then the top halfword, bits [31:16] of Rn is used.
If Y is B, then the bottom halfword, bits [15:0], of Rm is used.
If Y is T, then the top halfword, bits [31:16], of Rm is used.
If Y is B, then the bottom halfword (bits [15:0]) of Rm is used.
If Y is T, then the top halfword (bits [31:16]) of Rm is used.
R0, R4, R5 ; Multiplies the bottom halfword of R4 with the top
; halfword of R5, multiplies results and writes to R0
DocID022708 Rev 6
The STM32 Cortex-M4 instruction set
Conditional execution on page 64)
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