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/*********************************  atoi.as ***********************************
* Author:        Agner Fog
* date created:  2018-03-23
* Last modified: 2021-05-16
* Version:       1.11
* Project:       ForwardCom library libc.li
* Description:   atoi: convert string to integer
* C declaration: int64_t atoi(const char * str)
*
* Copyright 2018-2021 GNU General Public License http://www.gnu.org/licenses
*****************************************************************************/

code section execute align = 4                   // code section

_atoi function public reguse = 3, 0

if (int64 r0 == 0) {jump EMPTYEND}               // NULL pointer
push(r2, 4)                                      // save r2 - r4

int    r1 = 0                                    // state:  0: after whitespace
                                                 //         1: after +/-
                                                 //         2: after digit
int64  r2 = 0                                    // value
int    r3 = 0                                    // sign
int8   r4 = [r0]                                 // read first character from string
// loop through string until terminating zero
while (int8+ r4 != 0) {
   if (uint8+ r4 <= ' ') {                       // whitespace
      if (int r1 != 0) {jump ERROREND}           // space not allowed if state != 0. end of number
      jump NEXT                                  // else
   }
   if (uint8+ r4 <= '-') {                       // '+' or '-'
      if (int r1 != 0) {jump ERROREND}           // sign not allowed if state != 0. end of number
      int r1 = 1                                 // state = 1
      if (uint8+ r4 == '-') {
         int8+ r3 = 1                            // sign
         jump NEXT                               // else
      }
      if (uint8+ r4 != '+') {
         jump ERROREND                           // anything else than '+'. end of number
      }
   }
   else {
      int8+ r4 -= '0'                            // subtract ASCII '0'
      if (uint8+ r4 > 9) {jump ERROREND}         // anything else than 0-9. end of number
      int64 r2 *= 10                             // value * 10
      int64 r2 += r4                             // + digit
      int   r1 = 2                               // state = 2
   }
   NEXT:
   int64 r0++                                    // point to next character
   int8 r4 = [r0]                                // read next character from string
}
ERROREND:                                        // jump here when a character that cannot be part of the string is met
int64 r0 = r3 ? -r2 : r2                         // change sign if r3

pop(r2, 4)                                       // restore r2 - r4

EMPTYEND:
return

_atoi end

code end