stdlib/convert.pvvs

#ifndef VVS_STDLIB_CONVERT
#define VVS_STDLIB_CONVERT

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@ Name:
@   atoi (110000)
@ Description:
@   Convert null-terminated ASCII string to integer.
@   Result is negative if leading character is a hyphen ('-').
@   Result is positive if leading character is a plus sign ('+') or number.
@   Excluding the sign, parsing halts on the first non-numeric ASCII character.
@   Since all possible return values are valid, this subroutine simply returns
@   zero if no parseable number was found. Any stronger validity checks are the
@   responsibility of the caller. Similarly, no overflow checks are performed.
@   In addition to returning the parsed integer, also returns a pointer to the
@   first character after the parsed integer.
@ Call Stack:
@   pointer to first character  <-- TOS
@ Return Stack:
@   integer
@   pointer to last parsed character  <-- TOS
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#include <stack.pvvs>
#include <string.pvvs>
NSSVTTSSSSN             | Mark: 110000 (atoi)

@ Check the first character and create a 'sign' flag on the stack.
@ Update the pointer to point to the first numeric character.
SNS                     | DUP
TTT                     | LOAD
SSSSSTSTTSTN            | PUSH 45 (ASCII '-')
TSST                    | SUBTRACT
NTSSSTTSSSSSSSSSSSSN    | BRZ > 00110000 00000000 (found_minus_sign)
SNS                     | DUP
TTT                     | LOAD
SSSSSTSTSTTN            | PUSH 43 (ASCII '+')
TSST                    | SUBTRACT
NTSSSTTSSSSSSSSSSSTN    | BRZ > 00110000 00000001 (found_plus_sign)
NSNSSTTSSSSSSSSSSTSN    | JMP > 00110000 00000010 (found_digit)
NSSVSSTTSSSSSSSSSSSTN   | Mark: 00110000 00000001 (found_plus_sign)
SSSTN                   | PUSH +1
TSSS                    | ADD
NSSVSSTTSSSSSSSSSSTSN   | Mark: 00110000 00000010 (found_digit)
SSSTN                   | PUSH +1 (sign_flag)
SNT                     | SWAP
NSNSSTTSSSSSSSSSSTTN    | JMP > 00110000 00000011 (done_with_sign_flag)
NSSVSSTTSSSSSSSSSSSSN   | Mark: 00110000 00000000 (found_minus_sign)
SSSTN                   | PUSH +1
TSSS                    | ADD
SSTTN                   | PUSH -1 (sign_flag)
SNT                     | SWAP
NSSVSSTTSSSSSSSSSSTTN   | Mark: 00110000 00000011 (done_with_sign_flag)

@ Create an accumulator on the TOS.
SSSSN                   | PUSH 0 (accumulator)

@ Main loop examines string one character at a time, building result in accumulator.
@ TOS> accumulator, string_ptr, sign_flag
NSSVSSTTSSSSSSSSSTSSN   | Mark: 00110000 00000100 (atoi:main_loop)
SSSTSN                  | PUSH +2
NSTTTSSN                | JSR > 1100 (deepdup)
TTT                     | LOAD
SNS                     | DUP
NSTTSSSSTN              | JSR > 100001 (isdigit)
NTSSSTTSSSSSSSSSTSTN    | BRZ > 00110000 00000101 (found_end_of_number)
SSSSSTTSSSSN            | PUSH 48 (ASCII '0')
TSST                    | SUBTRACT
SNT                     | SWAP
SSSTSTSN                | PUSH 10
TSSN                    | MULTIPLY
TSSS                    | ADD
SNT                     | SWAP
SSSTN                   | PUSH 1
TSSS                    | ADD
SNT                     | SWAP
NSNSSTTSSSSSSSSSTSSN    | JMP > 00110000 00000100 (atoi:main_loop)

@ Clean up and return
@ TOS> character, accumulator, string_ptr, sign_flag
NSSVSSTTSSSSSSSSSTSTN   | Mark: 00110000 00000101 (found_end_of_number)
SNN                     | DROP
SSSTTN                  | PUSH 3
NSTTSTTN                | JSR > 1011 (stackrotatereverse)
TSSN                    | MULTIPLY
SNT                     | SWAP
NTN                     | RTS

#endif