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Fix reading the same symbol twice when using {f,}scanf()

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PR #924 appears to use `unget()` subtly incorrectly when parsing
floating point numbers. The rest of the code only uses `unget()`
immediately followed by `goto Done;` to return back the symbol that
can't possibly belong to the directive we're processing.

With floating-point, however, the ungot characters could very well
be valid for the *next* directive, so we will essentially read them
twice. It can't be seen in `sscanf()` tests because `unget()` is a
no-op there, but the test I added for `fscanf()` fails like this:

        ...
        EXPECT_EQ(0xDEAD, i1)
                need 57005 (or 0xdead) =
                 got 908973 (or 0x000ddead)
        ...
        EXPECT_EQ(0xBEEF, i2)
                need 48879 (or 0xbeef) =
                 got 769775 (or 0x000bbeef)

This means we read 0xDDEAD instead of 0xDEAD and 0xBBEEF instead of
0xBEEF. I checked that both musl and glibc read 0xDEAD/0xBEEF, as
expected.

Fix the failing test by removing the unneeded `unget()` calls.
This commit is contained in:
Ivan Komarov 2024-02-19 22:34:46 +01:00
parent d3ff48c63f
commit 5fa42012da
2 changed files with 33 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

6
libc/stdio/vcscanf.c
View file

@ -410,9 +410,6 @@ int __vcscanf(int callback(void *), //
goto Done; goto Done;
} }
} else { } else {
if (c != -1 && unget) {
unget(c, arg);
}
goto GotFloatingPointNumber; goto GotFloatingPointNumber;
} }
} else { } else {
@ -465,9 +462,6 @@ int __vcscanf(int callback(void *), //
Continue: Continue:
continue; continue;
Break: Break:
if (c != -1 && unget) {
unget(c, arg);
}
break; break;
} while ((c = BUFFER) != -1); } while ((c = BUFFER) != -1);
GotFloatingPointNumber: GotFloatingPointNumber:

33
test/libc/stdio/fscanf_test.c Normal file
View file

@ -0,0 +1,33 @@
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/math.h"
#include "libc/stdio/stdio.h"
#include "libc/testlib/testlib.h"
TEST(fscanf, test_readAfterFloat) {
FILE *f = fmemopen("infDEAD-.125e-2BEEF", 19, "r");
float f1 = 666.666f, f2 = f1;
int i1 = 666, i2 = i1;
EXPECT_EQ(4, fscanf(f, "%f%x%f%x", &f1, &i1, &f2, &i2));
EXPECT_TRUE(isinf(f1));
EXPECT_EQ(0xDEAD, i1);
EXPECT_EQ(-0.125e-2f, f2);
EXPECT_EQ(0xBEEF, i2);
fclose(f);
}