URL
https://opencores.org/ocsvn/forwardcom/forwardcom/trunk
Subversion Repositories forwardcom
[/] [forwardcom/] [libraries/] [multiply_int_light.as] - Rev 145
Go to most recent revision | Compare with Previous | Blame | View Log
/**************************** multiply_int_light.as **************************
* Author: Agner Fog
* date created: 2021-05-26
* Last modified: 2021-05-26
* Version: 1.11
* Project: ForwardCom library libc_light.li
* Description: multiply_int: multiply two 32-bit signed integers
* This function is for small CPUs with limited capabilities and no multiplication instruction
*
* Copyright 2021 GNU General Public License http://www.gnu.org/licenses
*****************************************************************************/
code section execute
_multiply_int function public reguse=1,0
// multiplies two 32 bit signed integers. no overflow check
// input r0, r1: factors
// save r1, r2, r3
int64 sp -= 3*8
int64 [sp] = r1
int64 [sp+8] = r2
int64 [sp+0x10] = r3
// get signs
int32 r2 = r0 < 0 // sign of r0
int32 r0 = -r0, mask = r2 // abs(r0)
int32 r3 = r1 < 0 // sign of r1
int32 r1 = -r1, mask = r3 // abs(r1)
int r3 ^= r2 // sign of product
// get the smallest factor in r1
if (uint32 r1 > r0) {
int32 r2 = r1
int32 r1 = r0
int32 r0 = r2
}
int32 r2 = 0 // summation of r0 multiplied by each bit in r1
while (int32 r1 != 0) { // multiplication loop
uint32 r2 += r0, mask = r1 // add r0 if bit 0 of r1
uint32 r1 >>= 1
uint32 r0 <<= 1
}
int32 r0 = r3 ? -r2 : r2 // apply sign
// restore r2, r3
int64 r1 = [sp]
int64 r2 = [sp+8]
int64 r3 = [sp+0x10]
int64 sp += 3*8
return
code end
Go to most recent revision | Compare with Previous | Blame | View Log