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/****************************  gets_light.as **********************************

* Author:        Agner Fog

* date created:  2021-05-25

* Last modified: 2021-07-20

* Version:       1.11

* Project:       ForwardCom library libc_light.li

* Description:   gets_s: Read a string from standard input until newline

* This version is for small CPUs with limited capabilities

* The following instructions are avoided: mul, div, push, pop, sys_call.

* Input comes directly from input port 8

* Output to stdout goes directly to output port 10

*

* C declaration:

* char *gets_s (char *string, size_t max_length);

*

* This function is defined in the C11 standard

* It will read a string from stdin until a newline or carriage return is

* encountered or the maximum length is reached.

* The input is echoed to standard output.

* The newline or carriage return is not included in the string.

* A terminating zero is always inserted at the end of the string.

* If the string length, including the terminating zero, exceeds max_length

* then the superfluous characters are discarded and it keeps reading until

* a newline or carriage return.

* This version does not raise any exception in case max_length is exceeded,

* but returns a truncated string.

* A NULL pointer is returned if any of the input parameters are zero.

* The C standard says that reading ends at newline, but Windows versions end

* at carriage return. This version supports both for the sake of compatibility.

*

* Copyright 2021 GNU General Public License http://www.gnu.org/licenses

*****************************************************************************/

// define input and output port numbers

%stdin_port = 8

%stdin_status_port = 9

%stdout_port = 10

code section execute

_gets_s function public reguse = 3, 0

  // save r2, r3

  int64 sp -= 2*8

  int64 [sp] = r2

  int64 [sp+8] = r3

  // check if parameters are valid

  if (int64 r0 == 0) {jump gets_s_error}         // error: null pointer or zero length

  if (int64 r1 == 0) {jump gets_s_error}         // error: zero length

  int64 r2 = r0                                  // point to current position in output buffer

  // loop until newline or maximum string length

  while (true) {

    // wait for input

    do {

      int16 r3 = input(r3, stdin_status_port)    // check if there is input

    }

    while (int r3 == 0);

    int8 r3 = input(r3, stdin_port)              // read one byte from input

    int8 output(r3, r3, stdout_port)             // echo input

    if (int r3 == 10) {break}                    // stop at newline

    //if (int r3 == 13) {break}                  // optionally stop at charriage return

    int64 r1--                                   // count down maximum length

    if (int64 r1 <= 0) {continue}                // length limit reached. keep reading until newline

    int8 [r2] = r3                               // store byte as character in output buffer

    int64 r2++                                   // increment string pointer

  }

  int  r3 = 0                                    // insert terminating zero

  int8 [r2] = r3

  gets_s_9:

  // restore r2, r3

  int64 r2 = [sp]

  int64 r3 = [sp+8]

  int64 sp += 2*8

  return

  gets_s_error:

  int r0 = 0

  jump gets_s_9

code end