ref: 7c55ca5fff01fa28b99a0717860848071fca80ce
parent: 2b5db0d9d451dafa70039dc0a668cde68e59d4f3
author: Ori Bernstein <ori@eigenstate.org>
date: Wed Dec 4 07:55:03 EST 2019
acme: Apply each -/+ only once (#156) When plumbing an address like `3-`, Acme selects line 1, and similarly `3+` selects line 5. The same problem can be observed for character addresses (`#123+`) but _not_ for ones like `+`, `.+` or `/foo/+`: The problem only occurs when a number is followed by a direction (`-`/`+`). Following along with the example `3-` through `address` (in addr.c): We read `3` into `c` and match the `case` on line 239. The `while` loop on line 242ff reads additional digits into `c` and puts the first non-digit back by decrementing the index `q`. Then we find the range for line 3 on line 251 and continue. On the next iteration, we set `prevc` to the last `c`, but since that part read ahead _into `c`_, `c` is currently the _next_ character we will read, `-`, and now `prevc` is too. Then in the case block (line 210) the condition on line 211 holds and Acme believes that it has read two `-` in sequence and modifies the range to account for the “first” `-`. The “second” `-` gets applied after the loop is done, on line 292. So the general problem is: While reading numbers, Acme reads the next character after the number into `c`. It decrements the counter to ensure it will read it again on the next iteration, but it still uses it to update `prevc`. This change solves the problem by reading digits into `nc` instead. This variable is used to similar effect in the block for directions (line 212) and fills the role of “local `c` that we can safely use to read ahead” nicely. (imported from plan9front a82a8b6368274d77d42f526e379b74e79c137e26)
--- a/sys/src/cmd/acme/addr.c
+++ b/sys/src/cmd/acme/addr.c
@@ -215,12 +215,12 @@
case '5': case '6': case '7': case '8': case '9':
n = c -'0';
while(q<q1){- c = (*getc)(a, q++);
- if(c<'0' || '9'<c){+ nc = (*getc)(a, q++);
+ if(nc<'0' || '9'<nc){q--;
break;
}
- n = n*10+(c-'0');
+ n = n*10+(nc-'0');
}
if(*evalp)
r = number(md, t, r, n, dir, size, evalp);