PM0214 datasheet(121/245 Pages) STMICROELECTRONICS

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PM0214

The STM32 Cortex-M4 instruction set

244

; with top halfword of R3, writes to R3

SMUSDX

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.

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.

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.

SMULW{Y} Signed multiply (word by halfword). Y specifies which halfword of the

source register Rm is used as the second multiply operand.

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.

•

‘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 operands

Operation

The SMULBB, SMULTB, SMULBT and SMULTT instructions interprets the values from Rn

and Rm as four signed 16-bit integers. These instructions:

Multiply the specified signed halfword, top or bottom, values from Rn and Rm.

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:

Multiply the first operand and the top, T suffix, or the bottom, B suffix, halfword of the

second operand.

Write the 32 signed most significant bits of the 48-bit result in the destination register.

Restrictions

Do not use SP and do not use PC.

Examples

SMULBT

R0, R4, R5 ; Multiplies the bottom halfword of R4 with the top

; halfword of R5, multiplies results and writes to R0

SMULBB

R0, R4, R5 ; Multiplies the bottom halfword of R4 with the bottom

; halfword of R5, multiplies results and writes to R0

SMULTT

R0, R4, R5 ; Multiplies the top halfword of R4 with the top

; halfword of R5, multiplies results and writes to R0

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