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/**************************** divide_int_light.as **************************
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* Author: Agner Fog
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* date created: 2021-05-26
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* Last modified: 2021-05-26
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* Version: 1.11
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* Project: ForwardCom library libc_light.li
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* Description: divide_int: divide two 32-bit signed integers
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* This function is for small CPUs with limited capabilities and no division
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* instruction. It returns the quotient and the remainder.
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* Returns INT_MIN if dividing by zero.
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*
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* Copyright 2021 GNU General Public License http://www.gnu.org/licenses
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*****************************************************************************/
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code section execute
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_divide_int function public reguse=3,0
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// divide two 32 bit signed integers. return quotient and remainder
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// input r0: dividend
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// input r1: divisor
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// output r0: r0 / r1
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// output r1: r0 % r1
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if (int32 r1 == 0) {jump divide_error} // check for division by 0
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// save r2 - r5
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int64 sp -= 4*8
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int64 [sp+0x00] = r2
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int64 [sp+0x08] = r3
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int64 [sp+0x10] = r4
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int64 [sp+0x18] = r5
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// get signs
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int32 r2 = r0 < 0 // sign of r0
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int32 r0 = -r0, mask = r2 // abs(r0)
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int32 r3 = r1 < 0 // sign of r1
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int32 r1 = -r1, mask = r3 // abs(r1)
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int r3 ^= r2 // sign of result
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int r2 = 0 // quotient calcuated in r2
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int r4 = bitscan(r0, 1) // number of significant bits in dividend
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int r5 = bitscan(r1, 1) // number of significant bits in divisor
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if (int r4 >= r5) {
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// division loop
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int r4 -= r5 // approximate number of significant bits in quotient
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int r1 <<= r4 // shift left divisor
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do { // loop r4 + 1 times
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uint32 r5 = r0 >= r1 // one bit of quotient
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int32 r0 -= r1, mask = r5 // subtract if bigger
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int32 r2 <<= 1 // shift left quotient
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int32 r2 |= r5 // add new bit
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uint32 r1 >>= 1 // shift right divisor
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int r4-- // loop counter
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} while (int r4 >= 0)
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}
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// quotient = r2, remainder = r0
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int32 r1 = r3 ? -r0 : r0 // apply sign to remainder
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int32 r0 = r3 ? -r2 : r2 // apply sign to quotient
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// restore r2 - r5
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int64 r2 = [sp+0x00]
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int64 r3 = [sp+0x08]
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int64 r4 = [sp+0x10]
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int64 r5 = [sp+0x18]
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int64 sp += 4*8
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return
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divide_error: // division by zero
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int32 r0 = 0x80000000 // return INT_MIN
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int32 r1 = 0
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return
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code end
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