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Code Issues Releases Wiki Activity

Clarify the relationship between indices.

This commit is contained in:
Raymond Hettinger 2004-10-01 15:14:39 +00:00
parent 61f05fb96d
commit 4ca4c7c8cc
1 changed files with 7 additions and 5 deletions
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12
Modules/collectionsmodule.c
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@ -7,7 +7,7 @@
All rights reserved.
*/
#define BLOCKLEN 46
#define BLOCKLEN 2
#define CENTER ((BLOCKLEN - 1) / 2)
/* A `dequeobject` is composed of a doubly-linked list of `block` nodes.
@ -24,17 +24,19 @@
*
* The indices, d.leftindex and d.rightindex are always in the range
* 0 <= index < BLOCKLEN.
* Their exact relationship is:
* (d.leftindex + d.len - 1) % BLOCKLEN == d.rightindex.
*
* Empty deques have d.len == 0; d.leftblock==d.rightblock;
* d.leftindex == CENTER+1; and d.rightindex == CENTER.
* Checking for d.len == 0 is the intended way to see whether d is empty.
*
* Whenever d.leftblock == d.rightblock,
* d.leftindex + d.len == d.rightindex + 1.
* d.leftindex + d.len - 1 == d.rightindex.
*
* However, when d.leftblock != rightblock, d.leftindex and d.rightindex
* are indices into distinct blocks and have no relationship to one
* another (for example, sometimes d.leftindex > d.rightindex).
* However, when d.leftblock != d.rightblock, d.leftindex and d.rightindex
* become indices into distinct blocks and either may be larger than the
* other.
*/
typedef struct BLOCK {