Mark Firsts hash table resizing policy tweaks
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@ -110,17 +110,17 @@ B memberOf_c1(B t, B x) {
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u32* xp = (u32*)xv;
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i8* rp; B r = m_i8arrv(&rp, n);
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usz log = 64 - CLZ(n);
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usz msl = (64 - CLZ(n+n/2)) + 1; if (msl>18) msl=18;
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usz sh = 32 - (msl<14? msl : 14); // Shift to fit to table
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usz msl = (64 - CLZ(n+n/2)) + 1; if (msl>20) msl=20;
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usz sh = 32 - (msl<14? msl : 12+(msl&1)); // Shift to fit to table
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usz sz = 1 << (32 - sh); // Initial size
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usz msz = 1 << msl; // Max sz
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usz b = 64; // Block size
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// Resize or abort if more than 1/2^thresh collisions/element
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#define THRESH sz==msz? 1 : sz>=(1<<13)? 2 : 3
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#define THRESH sz==msz? 1 : sz>=(1<<15)? 3 : 5
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usz thresh = THRESH;
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// Filling e slots past the end requires e*(e+1)/2 collisions, so
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// n entries with 1/2 each can fill <sqrt(n/4)
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usz ext = n<=b? n : b + (1 << ((log-2)/2));
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// n entries with 1/2 each can fill <sqrt(n)
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usz ext = n<=b? n : b + (1 << (log/2));
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TALLOC(u32, hash0, msz+ext); u32* hash = hash0 + msz-sz;
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u32 x0 = hash32(xp[0]); rp[0] = 1;
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for (u64 i = 0; i < sz+ext; i++) hash[i] = x0;
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@ -135,20 +135,26 @@ B memberOf_c1(B t, B x) {
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rp[i] = k != h;
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}
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if (i == n) break;
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if (cc >= e>>thresh) {
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if (sz == msz) break; // Abort
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// Resize hash
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usz m = 1 + (sz < msz/4);
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sh -= m;
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usz dif = sz; sz <<= m; dif = sz-dif;
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i64 dc = (i64)cc - (i>>thresh);
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if (dc >= 0) {
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if (sz == msz || (i < n/2 && sz >= 1<<18)) break; // Abort
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// Avoid resizing if close to the end
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if (cc<n/2 && (n-i)*dc < (i*((i64)n+i))>>(5+log-(32-sh))) continue;
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// Resize hash, factor of 4
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usz m = 2;
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usz dif = sz*((1<<m)-1);
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sh -= m; sz <<= m;
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hash -= dif;
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usz j = 0;
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cc = 0;
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for (; j < dif; j++) hash[j] = x0;
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for (; j < sz + ext; j++) {
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u32 h = hash[j]; if (h==x0) continue; hash[j] = x0;
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u32 k = h>>sh; while (hash[k]!=x0) k++;
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u32 k0 = h>>sh, k = k0; while (hash[k]!=x0) k++;
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cc += k-k0;
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hash[k] = h;
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}
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if (cc >= n/2) break;
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thresh = THRESH;
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}
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}
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