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Add prepass for bit simulation.

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nella 2026-05-25 12:49:29 +02:00
parent 04a1611346
commit 386e63ae20
2 changed files with 142 additions and 1 deletions
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79
kernel/bitsim.h Normal file
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#ifndef BITSIM_H
#define BITSIM_H
#include "kernel/modtools.h"
YOSYS_NAMESPACE_BEGIN
struct BitSim {
Module *module;
SigMap &sigmap;
ModWalker &modwalker;
dict<SigBit, uint64_t> sim_vals;
uint64_t rng_state;
BitSim(Module *m, SigMap &sm, ModWalker &mw)
: module(m), sigmap(sm), modwalker(mw), rng_state(1337) {}
uint64_t xorshift64() {
rng_state ^= rng_state << 13;
rng_state ^= rng_state >> 7;
rng_state ^= rng_state << 17;
return rng_state;
}
uint64_t eval_bit(SigBit b) {
SigBit mapped = sigmap(b);
if (mapped == State::S0) return 0ULL;
if (mapped == State::S1) return ~0ULL;
if (mapped == State::Sx || mapped == State::Sz) return 0ULL;
auto it = sim_vals.find(mapped);
if (it != sim_vals.end()) return it->second;
sim_vals[mapped] = 0;
uint64_t res = 0;
if (!modwalker.has_drivers(mapped)) {
res = xorshift64();
} else {
auto &drivers = modwalker.signal_drivers[mapped];
if (drivers.empty()) {
res = xorshift64();
} else {
auto driver = *drivers.begin();
Cell *cell = driver.cell;
if (cell->is_builtin_ff()) {
res = xorshift64();
} else if (cell->type == ID($_AND_)) {
res = eval_bit(cell->getPort(ID::A)[0]) & eval_bit(cell->getPort(ID::B)[0]);
} else if (cell->type == ID($_OR_)) {
res = eval_bit(cell->getPort(ID::A)[0]) | eval_bit(cell->getPort(ID::B)[0]);
} else if (cell->type == ID($_XOR_)) {
res = eval_bit(cell->getPort(ID::A)[0]) ^ eval_bit(cell->getPort(ID::B)[0]);
} else if (cell->type == ID($_NOT_)) {
res = ~eval_bit(cell->getPort(ID::A)[0]);
} else if (cell->type == ID($_MUX_)) {
uint64_t s = eval_bit(cell->getPort(ID::S)[0]);
uint64_t a = eval_bit(cell->getPort(ID::A)[0]);
uint64_t b = eval_bit(cell->getPort(ID::B)[0]);
res = (a & ~s) | (b & s);
} else if (cell->type == ID($mux)) {
uint64_t s = eval_bit(cell->getPort(ID::S)[0]);
uint64_t a = eval_bit(cell->getPort(ID::A)[driver.offset]);
uint64_t b = eval_bit(cell->getPort(ID::B)[driver.offset]);
res = (a & ~s) | (b & s);
} else {
res = xorshift64();
}
}
}
sim_vals[mapped] = res;
return res;
}
};
YOSYS_NAMESPACE_END
#endif