56 lines
1.5 KiB
C
56 lines
1.5 KiB
C
/**
|
|
* 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;
|
|
}
|