src/usr.bin/m4/eval.c - diff

Return to eval.c CVS log

Up to [local] / src / usr.bin / m4

version 1.68, 2010/09/07 19:58:09

version 1.69, 2011/03/24 11:23:08

Line 880

* map every character of s1 that is specified in from

* into s3 and replace in s. (source s1 remains untouched)

* This is a standard implementation of map(s,from,to) function of ICON

* This is derived from the a standard implementation of map(s,from,to)

* language. Within mapvec, we replace every character of "from" with

* function of ICON language. Within mapvec, we replace every character

* the corresponding character in "to". If "to" is shorter than "from",

* of "from" with the corresponding character in "to".

* than the corresponding entries are null, which means that those

* If "to" is shorter than "from", than the corresponding entries are null,

* characters dissapear altogether. Furthermore, imagine

* which means that those characters dissapear altogether.

* map(dest, "sourcestring", "srtin", "rn..*") type call. In this case,

* `s' maps to `r', `r' maps to `n' and `n' maps to `*'. Thus, `s'

* ultimately maps to `*'. In order to achieve this effect in an efficient

* manner (i.e. without multiple passes over the destination string), we

* loop over mapvec, starting with the initial source character. if the

* character value (dch) in this location is different than the source

* character (sch), sch becomes dch, once again to index into mapvec, until

* the character value stabilizes (i.e. sch = dch, in other words

* mapvec[n] == n). Even if the entry in the mapvec is null for an ordinary

* character, it will stabilize, since mapvec[0] == 0 at all times. At the

* end, we restore mapvec* back to normal where mapvec[n] == n for

* 0 <= n <= 127. This strategy, along with the restoration of mapvec, is

* about 5 times faster than any algorithm that makes multiple passes over

* destination string.

static void

map(char *dest, const char *src, const char *from, const char *to)

Line 958

Line 944

while (*src) {

sch = (unsigned char)(*src++);

dch = mapvec[sch];

while (dch != sch) {

sch = dch;

dch = mapvec[sch];

}

if ((*dest = (char)dch))

dest++;

}