offsets.h File Reference

Functions for extraction of offset lists of subarrays. More...

#include "utils.h"

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Functions
int	get_array_offsets (off_t **offs, size_t *noffs, int dim, const IPNT gs, const IPNT gn, const IPNT ls, const IPNT ln)
	computes offsets into a subarray.

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Detailed Description

Functions for extraction of offset lists of subarrays.

Compute offsets for a subarray with starts ls and lengths ln of a global array with starts gs and lengths gn. Dimension of both assumed to be dim.

number of offsets = product of ln[1]*...*ln[dim-1].

For each offset j,

• figure out the index array idx:

  idx[dim-1]=j/(ln[1]*...*ln[dim-2]), remainder k=j-idx[dim-1]*ln[1]*...*ln[dim-2]

  for j=dim-2,j>0: idx[j]=k/(ln[1]*...*ln[j-1]), k=k-idx[j]*ln[1]*...*ln[j-1]

• construct the offset in the global array:

  offs[j]=sum from i=0:dim-1 (idx[i]+ls[i]-gs[i])*gn[0]*...*gn[i-1]

Example: suppose dim=2, gs=[0,0], gn=[4,4], ls=[1,1], ln=[2,2]. The subarray consists of the four points [1,1],[2,1],[1,2], and [2,2]. The offsets are clearly 5 and 9, noffs=2 = ln[1]*...*ln[dim-1].

To work out the 2nd offset (j=1), product of ln[dim-2]*...*ln[1]=1 (empty products are by default = 1). 1/1=1, remainder is 0. So idx=[0,1].

2nd offset = (idx[0]+ls[0]-gs[0]) (idx[1]+ls[1]-gs[1])*gn[0] = (0+1-0)+(1+1-0)*4=9

Definition in file offsets.h.

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Function Documentation

get_array_offsets	(	off_t **	offs,
		size_t *	noffs,
		int	dim,
		const IPNT	gs,
		const IPNT	gn,
		const IPNT	ls,
		const IPNT	ln
	)

computes offsets into a subarray.

same as

See also:

get_array_offsets,

but uses off_t, size_t instead of explicit types.

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