gcd.c

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/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2026 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */
 
/**
 * @file gcd.c
 * @brief Implements the OP_GCD opcode for greatest common divisor.
 *
 * Behavior:
 * - Pops two numeric operands (a, b). Floats are truncated to int64.
 * - Computes gcd(|a|, |b|) using Euclid's algorithm.
 * - Pushes VAL_INT result.
 *
 * Stack effect:
 * - Pop: b, a
 * - Push: gcd(a, b)
 *
 * Types:
 * - Accepts VAL_INT and VAL_FLOAT; others cause a runtime error.
 */
 
case OP_GCD: {
  Value vb = pop_value(vm);
  Value va = pop_value(vm);
  if (!((va.type == VAL_INT) || (va.type == VAL_FLOAT)) ||
      !((vb.type == VAL_INT) || (vb.type == VAL_FLOAT))) {
    fprintf(stderr, "Runtime type error: GCD expects numbers, got %s and %s\n",
            value_type_name(va.type), value_type_name(vb.type));
    exit(1);
  }
  int64_t a = (va.type == VAL_INT) ? va.i : (int64_t)va.d;
  int64_t b = (vb.type == VAL_INT) ? vb.i : (int64_t)vb.d;
  if (a == INT64_MIN)
    a = (int64_t)INT64_MAX;
  else if (a < 0)
    a = -a;
  if (b == INT64_MIN)
    b = (int64_t)INT64_MAX;
  else if (b < 0)
    b = -b;
  while (b != 0) {
    int64_t t = a % b;
    a = b;
    b = t;
  }
  Value res = make_int(a);
  free_value(va);
  free_value(vb);
  push_value(vm, res);
  break;
}