Basic MergeShuffle implementation (slow merge)
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@ -431,13 +431,43 @@ B rand_deal_c1(B t, B x) {
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if (xi==0) return emptyIVec();
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RAND_START;
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i32* rp; B r = m_i32arrv(&rp, xi);
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for (i64 i = 0; i < xi; i++) rp[i] = i;
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for (i64 i = 0; i < xi; i++) {
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i32 j = wy2u0k(wyrand(&seed), xi-i) + i;
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i32 c = rp[j];
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rp[j] = rp[i];
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rp[i] = c;
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// MergeShuffle
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usz sh = 0;
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usz thr = 1<<24;
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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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for (usz p = 0, i = 0; p < q; p++) {
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usz e = (n*(p+1)) >> sh;
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for (usz k = i; k < e; k++) rp[k] = k;
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for (; i < e; i++) {
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usz j = wy2u0k(wyrand(&seed), e-i) + i;
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usz c=rp[j]; rp[j]=rp[i]; rp[i]=c;
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}
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}
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for (usz w = 1; w < q; w <<= 1) {
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usz i = 0;
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for (usz p = 0; p < q; p += 2*w) {
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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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}
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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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}
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}
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}
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RAND_END;
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return r;
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}
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