void cut2(int N, int M) {
// printf("cut2 %d %d \n", N, M);
int L = M - N;
if ( L < cut2Limit ) {
quicksort0(N, M);
return;
}
int depthLimit = 2 * floor(log(L));
cut2c(N, M, depthLimit);
} // end cut2
// cut2 is used as a best in class quicksort implementation
// with a defense against quadratic behavior due to duplicates
// cut2 is a support function to call up the workhorse cut2c
void cut2(void **A, int N, int M, int (*compare)()) {
// printf("cut2 %d %d %d\n", N, M, M-N);
int L = M - N;
if ( L < cut2Limit ) {
quicksort0(A, N, M, compare);
return;
}
int depthLimit = 1 + 2.5 * floor(log(L));
cut2c(A, N, M, depthLimit, compare);
} // end cut2
void cut2c(int N, int M, int depthLimit) {
int L;
Start:
if ( depthLimit <= 0 ) {
heapc(A, N, M);
return;
}
L = M - N;
if ( L < cut2Limit ) {
quicksort0c(N, M, depthLimit);
return;
}
depthLimit--;
// Check for duplicates
int sixth = (M - N + 1) / 6;
int e1 = N + sixth;
int e5 = M - sixth;
int e3 = (N+M) / 2; // The midpoint
int e4 = e3 + sixth;
int e2 = e3 - sixth;
// Sort these elements using a 5-element sorting network
void *ae1 = A[e1], *ae2 = A[e2], *ae3 = A[e3], *ae4 = A[e4], *ae5 = A[e5];
void *t;
// if (ae1 > ae2) { t = ae1; ae1 = ae2; ae2 = t; }
if ( compareXY(ae1, ae2) > 0 ) { t = ae1; ae1 = ae2; ae2 = t; }
if ( compareXY(ae4, ae5) > 0 ) { t = ae4; ae4 = ae5; ae5 = t; }
if ( compareXY(ae1, ae3) > 0 ) { t = ae1; ae1 = ae3; ae3 = t; }
if ( compareXY(ae2, ae3) > 0 ) { t = ae2; ae2 = ae3; ae3 = t; }
if ( compareXY(ae1, ae4) > 0 ) { t = ae1; ae1 = ae4; ae4 = t; }
if ( compareXY(ae3, ae4) > 0 ) { t = ae3; ae3 = ae4; ae4 = t; }
if ( compareXY(ae2, ae5) > 0 ) { t = ae2; ae2 = ae5; ae5 = t; }
if ( compareXY(ae2, ae3) > 0 ) { t = ae2; ae2 = ae3; ae3 = t; }
if ( compareXY(ae4, ae5) > 0 ) { t = ae4; ae4 = ae5; ae5 = t; }
A[e1] = ae1; A[e2] = ae2; A[e3] = ae3; A[e4] = ae4; A[e5] = ae5;
// Fix end points
if ( compareXY(ae1, A[N]) < 0 ) iswap(N, e1, A);
if ( compareXY(A[M], ae5) < 0 ) iswap(M, e5, A);
int duplicate = -1;
// if ( ae1, ae5 ) { duplicate = e1; } else
if ( compareXY(ae1, ae5) == 0 ) { duplicate = e1; } else
if ( compareXY(ae1, ae4) == 0 ) { duplicate = e1; } else
if ( compareXY(ae2, ae5) == 0 ) { duplicate = e2; } else
if ( compareXY(ae1, ae3) == 0 ) { duplicate = e1; } else
if ( compareXY(ae2, ae4) == 0 ) { duplicate = e2; } else
if ( compareXY(ae3, ae5) == 0 ) { duplicate = e3; } else
if ( compareXY(ae1, ae2) == 0 ) { duplicate = e1; } else
if ( compareXY(ae2, ae3) == 0 ) { duplicate = e2; } else
if ( compareXY(ae3, ae4) == 0 ) { duplicate = e3; } else
if ( compareXY(ae4, ae5) == 0 ) { duplicate = e4; };
if ( 0 <= duplicate ) {
void cut2c();
cut3duplicates(N, M, duplicate, cut2c, depthLimit);
return;
}
register void *T = ae3; // pivot
// test to play safe:
// if ( T <= A[N] || A[M] < T ) {
if ( compareXY(T, A[N]) <= 0 || compareXY(A[M], T) < 0 ) {
// give up because cannot find a good pivot
quicksort0c(N, M, depthLimit+1);
return;
}
register int I, J; // indices
register void *AI, *AJ; // array values
// initialize running indices
I= N;
J= M;
// The left segment has elements < T
// The right segment has elements >= T
Left:
I = I + 1;
AI = A[I];
// if (AI < T) goto Left;
if ( compareXY( AI, T) < 0 ) goto Left;
Right:
J = J - 1;
AJ = A[J];
// if ( T <= AJ ) goto Right;
if ( compareXY( T, AJ) <= 0 ) goto Right;
if ( I < J ) {
A[I] = AJ; A[J] = AI;
goto Left;
}
if ( (I - N) < (M - J) ) { // smallest one first
cut2c(N, J, depthLimit);
N = I;
goto Start;
}
cut2c(I, M, depthLimit);
M = J;
goto Start;
} // (* OF cut2; *) ... the brackets reminds that this was Pascal code
