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107 lines
2.7 KiB
107 lines
2.7 KiB
/*!
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\file util.c
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\brief Various utility routines
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\date Started 4/12/2007
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\author George
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\version\verbatim $Id: gk_util.c 16223 2014-02-15 21:34:09Z karypis $ \endverbatim
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*/
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#include <GKlib.h>
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/*************************************************************************
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* This file randomly permutes the contents of an array.
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* flag == 0, don't initialize perm
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* flag == 1, set p[i] = i
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**************************************************************************/
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void gk_RandomPermute(size_t n, int *p, int flag)
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{
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size_t i, u, v;
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int tmp;
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if (flag == 1) {
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for (i=0; i<n; i++)
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p[i] = i;
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}
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for (i=0; i<n/2; i++) {
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v = RandomInRange(n);
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u = RandomInRange(n);
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gk_SWAP(p[v], p[u], tmp);
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}
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}
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/************************************************************************/
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/*!
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\brief Converts an element-based set membership into a CSR-format set-based
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membership.
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For example, it takes an array such as part[] that stores where each
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element belongs to and returns a pair of arrays (pptr[], pind[]) that
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store in CSF format the list of elements belonging in each partition.
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\param n
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the number of elements in the array (e.g., # of vertices)
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\param range
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the cardinality of the set (e.g., # of partitions)
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\param array
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the array that stores the per-element set membership
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\param ptr
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the array that will store the starting indices in ind for
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the elements of each set. This is filled by the routine and
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its size should be at least range+1.
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\param ind
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the array that stores consecutively which elements belong to
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each set. The size of this array should be n.
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*/
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/************************************************************************/
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void gk_array2csr(size_t n, size_t range, int *array, int *ptr, int *ind)
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{
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size_t i;
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gk_iset(range+1, 0, ptr);
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for (i=0; i<n; i++)
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ptr[array[i]]++;
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/* Compute the ptr, ind structure */
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MAKECSR(i, range, ptr);
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for (i=0; i<n; i++)
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ind[ptr[array[i]]++] = i;
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SHIFTCSR(i, range, ptr);
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}
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/*************************************************************************
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* This function returns the log2(x)
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**************************************************************************/
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int gk_log2(int a)
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{
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size_t i;
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for (i=1; a > 1; i++, a = a>>1);
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return i-1;
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}
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/*************************************************************************
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* This function checks if the argument is a power of 2
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**************************************************************************/
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int gk_ispow2(int a)
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{
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return (a == (1<<gk_log2(a)));
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}
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/*************************************************************************
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* This function returns the log2(x)
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**************************************************************************/
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float gk_flog2(float a)
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{
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return log(a)/log(2.0);
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}
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