M2compiler-V3/runtime/syslib/shim.c

/* m2compiler-V3 runtime shim (C).
 *
 * Bridges Modula-2 external procedures to the host. Memory layout
 * matches the compiler's: a STRING (ARRAY OF CHAR) value is a
 * descriptor [0] = LONGCARD element count, then the bytes; the
 * compiler passes the descriptor's address as an `l`.
 *
 * Linked with every V3 program image.
 */

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

/* Write the contents of a string descriptor to fd 1. Returns the
   number of bytes written. */
long m2write(long *desc)
{
    long n = desc[0];
    if (n > 0)
        write(1, (char *)(desc + 1), (size_t)n);
    return n;
}

/* Write a newline to fd 1. */
long m2writeln(void)
{
    write(1, "\n", 1);
    return 0;
}

/* Read one character from stdin (0 at EOF). */
long m2readchar(void)
{
    int c = getchar();
    return (c == EOF) ? 0 : c;
}

/* Read a signed decimal integer from stdin, skipping leading
   whitespace. The first non-digit after the number is consumed. */
long m2readint(void)
{
    long v = 0;
    int c;
    int neg = 0;

    do { c = getchar(); } while (c == ' ' || c == '\t' ||
                                 c == '\n' || c == '\r');
    if (c == '-') { neg = 1; c = getchar(); }
    while (c >= '0' && c <= '9') {
        v = v * 10 + (c - '0');
        c = getchar();
    }
    return neg ? -v : v;
}

/* Set a string descriptor's logical length (header). */
long m2setlen(long *desc, long n)
{
    desc[0] = n;
    return n;
}

/* Write a single character (byte) to fd 1. */
long m2writechar(long c)
{
    char ch = (char)c;
    write(1, &ch, 1);
    return 0;
}

/* Write a signed decimal integer to fd 1. */
long m2writeint(long v)
{
    char buf[32];
    int i = 0;
    int neg = 0;
    unsigned long u;

    if (v < 0) { neg = 1; u = (unsigned long)(-v); }
    else u = (unsigned long)v;

    do { buf[i++] = (char)('0' + (u % 10)); u /= 10; } while (u != 0);
    if (neg) buf[i++] = '-';
    while (i > 0)
        write(1, &buf[--i], 1);
    return 0;
}

/* Terminate the process. */
long m2exit(long code)
{
    exit((int)code);
    return 0;
}