log.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 log.c
 * @brief Implements the OP_LOG opcode using C99 math.h log() (natural logarithm).
 *
 * Behavior:
 * - Pops one numeric operand (int or float).
 * - If x <= 0, pushes NaN to indicate domain error; otherwise pushes ln(x).
 * - Result type is VAL_FLOAT.
 *
 * Stack effect:
 * - Pop: x
 * - Push: ln(x) | NaN
 *
 * Types:
 * - Accepts VAL_INT and VAL_FLOAT; errors on others.
 */
 
#include <math.h>
 
case OP_LOG: {
  Value v = pop_value(vm);
  if (v.type == VAL_INT || v.type == VAL_FLOAT) {
    double x = (v.type == VAL_FLOAT) ? v.d : (double)v.i;
    if (x <= 0.0) {
      /* Domain error: return NaN to signal invalid input */
      push_value(vm, make_float(NAN));
    } else {
      double r = log(x);
      push_value(vm, make_float(r));
    }
    free_value(v);
  } else {
    fprintf(stderr, "Runtime type error: LOG expects number, got %s\n", value_type_name(v.type));
    exit(1);
  }
  break;
}