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Check overflow condition is power of 2 without using int32

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This commit is contained in:
Eddie Hung 2019-09-18 12:16:03 -07:00
parent c9fe4d7992
commit 347cbf59bd
2 changed files with 15 additions and 5 deletions
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16
passes/pmgen/xilinx_dsp.cc
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@ -337,10 +337,20 @@ void pack_xilinx_dsp(dict<SigBit, Cell*> &bit_to_driver, xilinx_dsp_pm &pm)
cell->setParam("\\SEL_MASK", Const("MASK"));
if (st.overflow->type == "$ge") {
int B = st.overflow->getPort("\\B").as_int();
log_assert((B & (B-1)) == 0); // Exact power of 2
Const B = st.overflow->getPort("\\B").as_const();
log_assert(std::count(B.bits.begin(), B.bits.end(), State::S1) == 1);
// Since B is an exact power of 2, subtract 1
// by inverting all bits up until hitting
// that one hi bit
for (auto &b : B.bits)
if (b == State::S0) b = State::S1;
else if (b == State::S1) {
b = State::S0;
break;
}
B.extu(48);
cell->setParam("\\MASK", Const(B-1, 48));
cell->setParam("\\MASK", B);
cell->setParam("\\PATTERN", Const(0, 48));
cell->setPort("\\OVERFLOW", st.overflow->getPort("\\Y"));
}