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Optimize X check in vector subarray 

Optimize check for X bits while doing vector4 subarray. In particular,
do X checks a word at a time so that individual bits need not be tested.
This commit is contained in:
Stephen Williams 2007-12-04 22:16:31 -08:00
parent 3b90a827e5
commit 19e8c05788
1 changed files with 24 additions and 4 deletions
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28
vvp/vvp_net.cc
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@ -353,22 +353,42 @@ unsigned long* vvp_vector4_t::subarray(unsigned adr, unsigned wid) const
/* Get the first word we are scanning. We may in fact be
somewhere in the middle of that word. */
unsigned long tmp = bits_ptr_[adr/BITS_PER_WORD];
tmp >>= 2UL * (adr%BITS_PER_WORD);
unsigned long off = adr%BITS_PER_WORD;
tmp >>= 2UL * off;
// Test for X bits but not beyond the desired wid.
unsigned long xmask = WORD_X_BITS;
if (wid < (BITS_PER_WORD-off))
xmask &= ~(-1UL << 2*wid);
if (tmp & xmask)
goto x_out;
// Where in the target array to write the next bit.
unsigned long mask1 = 1;
const unsigned long mask1_last = 1UL << (BIT2_PER_WORD-1);
unsigned long*val_ptr = val;
// Track where the source bit is in the source word.
unsigned adr_bit = adr%BITS_PER_WORD;
// Scan...
for (unsigned idx = 0 ; idx < wid ; idx += 1) {
/* Starting a new word? */
if (adr%BITS_PER_WORD == 0)
if (adr_bit == BITS_PER_WORD) {
tmp = bits_ptr_[adr/BITS_PER_WORD];
// If this is the last word, then only test
// for X in the valid bits.
xmask = WORD_X_BITS;
if ((wid-idx) < BITS_PER_WORD)
xmask &= ~(WORD_Z_BITS<<2*(wid-idx));
if (tmp & xmask)
goto x_out;
adr_bit = 0;
}
if (tmp&2)
goto x_out;
if (tmp&1)
*val_ptr |= mask1;
adr += 1;
adr_bit += 1;
tmp >>= 2UL;
if (mask1 == mask1_last) {