Only iterate over set bits in random merge
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@ -434,7 +434,7 @@ B rand_deal_c1(B t, B x) {
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// MergeShuffle
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usz sh = 0;
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usz thr = 1<<24;
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usz thr = 1<<18;
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while ((xi >> sh) > thr) sh++;
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usz q = 1 << sh;
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u64 n = xi;
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@ -454,13 +454,16 @@ B rand_deal_c1(B t, B x) {
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usz t = i;
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usz j = (n*(p + w)) >> sh;
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usz e = (n*(p + 2*w)) >> sh;
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u64 r = wyrand(&seed); // Random bits
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while (1) {
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u64 bit = r&1; r>>=1;
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if (bit) { if (j == e) break; usz c=rp[i]; rp[i]=rp[j]; rp[j]=c; j++; }
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else { if (i == j) break; }
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if (++i%64==0) r = wyrand(&seed);
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for (usz i0 = i; ; i0 += 64) {
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for (u64 r = wyrand(&seed); r; r&=r-1) {
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i = i0 + CTZ(r);
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if (i > j) { i=j; goto tail; }
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if (j == e) goto tail;
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usz c=rp[j]; rp[j]=rp[i]; rp[i]=c;
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j++;
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}
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}
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tail:
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for (; i < e; i++) {
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usz j = wy2u0k(wyrand(&seed), 1+i-t) + t;
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usz c=rp[j]; rp[j]=rp[i]; rp[i]=c;
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