Atmel AVR - 83 MULSU - Multiply Signed with Unsigned; Description; Status Register (SREG) and Boolean Formula

83. MULSU – Multiply Signed with Unsigned
83.1. Description
This instruction performs 8-bit × 8-bit → 16-bit multiplication of a signed and an unsigned number.
Rd Rr R1 R0
Multiplicand Multiplier
→
Product High Product Low
8 8 16
The multiplicand Rd and the multiplier Rr are two registers. The multiplicand Rd is a signed number, and
the multiplier Rr is unsigned. The 16-bit signed product is placed in R1 (high byte) and R0 (low byte).
This instruction is not available in all devices. Refer to the device specific instruction set summary.
Operation:
(i) R1:R0 ← Rd × Rr (signed ← signed × unsigned)
Syntax: Operands: Program Counter:
(i) MULSU Rd,Rr 16 ≤ d ≤ 23, 16 ≤ r ≤ 23 PC ← PC + 1
16-bit Opcode:
0000 0011 0ddd 0rrr
83.2. Status Register (SREG) and Boolean Formula
I T H S V N Z C
– – – – – – ⇔ ⇔
C R15
Z R15 • R14 • R13 • R12 • R11 • R10 • R9 • R8R7 • R6 • R5 • R4 • R3 • R2 • R1 • R0
Set if the result is $0000; cleared otherwise.
R (Result) equals R1,R0 after the operation.
Example:
;******************************************************************************
;* DESCRIPTION
;* Signed multiply of two 16-bit numbers with 32-bit result.
;* USAGE
;* r19:r18:r17:r16 = r23:r22 * r21:r20
;******************************************************************************
muls16x16_32:
clr r2
muls r23, r21 ; (signed)ah * (signed)bh
movw r19:r18, r1:r0
mul r22, r20 ; al * bl
movw r17:r16, r1:r0
mulsu r23, r20 ; (signed)ah * bl
Atmel AVR Instruction Set Manual [OTHER]
Atmel-0856L-AVR-Instruction-Set-Manual_Other-11/2016
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