1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
|
; 32-bit by 32-bit multiplication routine for use with C
AREA |mul64$$code|, CODE, READONLY
|x$codeseg|
EXPORT mul64
; On entry a1 and a2 contain the 32-bit integers to be multiplied (a, b)
; On exit a1 and a2 contain the result (a1 bits 0-31, a2 bits 32-63)
mul64
MOV ip, a1, LSR #16 ; ip = a_hi
MOV a4, a2, LSR #16 ; a4 = b_hi
BIC a1, a1, ip, LSL #16 ; a1 = a_lo
BIC a2, a2, a4, LSL #16 ; a2 = b_lo
MUL a3, a1, a2 ; a3 = a_lo * b_lo (m_lo)
MUL a2, ip, a2 ; a2 = a_hi * b_lo (m_mid1)
MUL a1, a4, a1 ; a1 = a_lo * b_hi (m_mid2)
MUL a4, ip, a4 ; a4 = a_hi * b_hi (m_hi)
ADDS ip, a2, a1 ; ip = m_mid1 + m_mid2 (m_mid)
ADDCS a4, a4, #&10000 ; a4 = m_hi + carry (m_hi')
ADDS a1, a3, ip, LSL #16 ; a1 = m_lo + (m_mid<<16)
ADC a2, a4, ip, LSR #16 ; a2 = m_hi' + (m_mid>>16) + carry
MOV pc, lr
END
|
