/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */

/**
 * @file sclamp.c
 * @brief Implements the OP_SCLAMP opcode for signed N-bit two's-complement wrapping.
 *
 * This VM opcode wraps an integer into the signed N-bit range using two's
 * complement semantics. It first masks to N bits and then sign-extends if the
 * sign bit is set, yielding a value in the range [-2^(N-1) .. 2^(N-1)-1].
 * N is provided by the instruction operand.
 *
 * Stack contract:
 * - Pops: value (int)
 * - Pushes: value (int)
 */

case OP_SCLAMP: {
  /* Two's complement wrap to signed N-bit range:
     - Mask to N bits
     - If sign bit is set, sign-extend to 64-bit
     This yields values in [-2^(N-1) .. 2^(N-1)-1]. */
  Value v = pop_value(vm);
  int bits = inst.operand;
  int64_t vi = (v.type == VAL_INT) ? v.i : 0;

  int64_t out = 0;
  if (bits <= 0) {
    out = 0;
  } else {
    uint64_t mask = (bits >= 64) ? UINT64_MAX : ((1ULL << bits) - 1ULL);
    uint64_t wrapped = ((uint64_t)vi) & mask;
    if (bits >= 64) {
      /* 64-bit: already full width; interpret as signed */
      out = (int64_t)wrapped;
    } else {
      uint64_t sign_bit = 1ULL << (bits - 1);
      if (wrapped & sign_bit) {
        /* sign-extend */
        out = (int64_t)(wrapped | (~mask));
      } else {
        out = (int64_t)wrapped;
      }
    }
  }

  push_value(vm, make_int(out));
  free_value(v);
  break;
}