56 lines
1.5 KiB
C
56 lines
1.5 KiB
C
/*
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* This file is part of the Fun programming language.
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* https://fun-lang.xyz/
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*
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* Copyright 2025 Johannes Findeisen <you@hanez.org>
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* Licensed under the terms of the Apache-2.0 license.
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* https://opensource.org/license/apache-2-0
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*/
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/**
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* @file sclamp.c
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* @brief Implements the OP_SCLAMP opcode for signed N-bit two's-complement wrapping.
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*
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* This VM opcode wraps an integer into the signed N-bit range using two's
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* complement semantics. It first masks to N bits and then sign-extends if the
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* sign bit is set, yielding a value in the range [-2^(N-1) .. 2^(N-1)-1].
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* N is provided by the instruction operand.
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*
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* Stack contract:
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* - Pops: value (int)
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* - Pushes: value (int)
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*/
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case OP_SCLAMP: {
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/* Two's complement wrap to signed N-bit range:
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- Mask to N bits
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- If sign bit is set, sign-extend to 64-bit
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This yields values in [-2^(N-1) .. 2^(N-1)-1]. */
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Value v = pop_value(vm);
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int bits = inst.operand;
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int64_t vi = (v.type == VAL_INT) ? v.i : 0;
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int64_t out = 0;
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if (bits <= 0) {
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out = 0;
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} else {
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uint64_t mask = (bits >= 64) ? UINT64_MAX : ((1ULL << bits) - 1ULL);
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uint64_t wrapped = ((uint64_t)vi) & mask;
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if (bits >= 64) {
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/* 64-bit: already full width; interpret as signed */
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out = (int64_t)wrapped;
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} else {
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uint64_t sign_bit = 1ULL << (bits - 1);
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if (wrapped & sign_bit) {
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/* sign-extend */
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out = (int64_t)(wrapped | (~mask));
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} else {
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out = (int64_t)wrapped;
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}
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}
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}
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push_value(vm, make_int(out));
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free_value(v);
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break;
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}
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