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50133: use read-ahead and lseek-rewind for efficient line-buffered input

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This commit is contained in:
Bart Schaefer 2022-04-28 21:06:51 -07:00
parent 007c7df74a
commit df0c783f4b
3 changed files with 86 additions and 1 deletions
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24
Src/input.c
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@ -217,12 +217,34 @@ shinbufrestore(void)
static int
shingetchar(void)
{
int nread;
int nread, rsize = isset(SHINSTDIN) ? 1 : SHINBUFSIZE;
if (shinbufptr < shinbufendptr)
return STOUC(*shinbufptr++);
shinbufreset();
#ifdef USE_LSEEK
if (rsize == 1 && lseek(SHIN, 0, SEEK_CUR) != (off_t)-1)
rsize = SHINBUFSIZE;
if (rsize > 1) {
do {
errno = 0;
nread = read(SHIN, shinbuffer, rsize);
} while (nread < 0 && errno == EINTR);
if (nread <= 0)
return -1;
if (isset(SHINSTDIN) &&
(shinbufendptr = memchr(shinbuffer, '\n', nread))) {
shinbufendptr++;
rsize = (shinbufendptr - shinbuffer);
if (nread > rsize &&
lseek(SHIN, -(nread - rsize), SEEK_CUR) < 0)
zerr("lseek(%d, %d): %e", SHIN, -(nread - rsize), errno);
} else
shinbufendptr = shinbuffer + nread;
return STOUC(*shinbufptr++);
}
#endif
for (;;) {
errno = 0;
nread = read(SHIN, shinbufendptr, 1);