On 13/06/12 05:26, Morgan L. Owens wrote: > After reading the performance improvements RFC about interned strings, > and its passing mention of a "special data structure (e.g. > zend_string) instead of char*", I've been thinking a little bit about > this and what such a structure could be. > > But rather than interned strings, I thought that _implicit_ > concatenation would be a bigger win in the long term. Like interning, > it relies on strings being immutable. > > This zend_string is a composite type. Leaves are _almost_ identical to > existing string zvals - char* val, int len - but also an additional > "child_count" field. For leaves, child_count is zero (not incidentally > indicating that it _is_ a leaf). For internal nodes, "val" is a list > of zend_strings (child_count of them). "len" still refers to the total > string length (the sum of the len fields of its children). > > So a string that has been built up through concatenation is > represented by a tree (actually a dag) of zend_strings. The edges in > this dag are all properly reference-counted; discarding a string > decrements the reference counts of its children. How do you list then? As a single-linked list? That would avoid reuse of the component strings in different superstrings except from matching ends...
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