sclamp.c

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/*
 * 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
 */


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;
}