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Fix printf precision/field width being limited by internal buffer size (#799)

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The C standard, when defining field width and precision, never gives
any limit on the values used for them (except, I believe, that they
fit within an int). In other words, if the user gives a field width of
32145 and a precision of 9218, the implementation has to handle these
values correctly. However, when such kinds of high numbers are used
with integer conversions, cosmopolitan is limited by an internal
buffer size of 144, which means precisions and field widths have to
fit within this, which violates the standard.

This means that for example, the following program:

 #include <stdio.h>
 #include <string.h>

int main()
{
    char buf2[512] = {};

    int i = snprintf(buf2, sizeof(buf2), "%.9999u", 10);
    printf("%d %zu\n", i, strlen(buf2));
}

would, instead of printing "9999 511" (the correct output), instead
print "144 144" under cosmopolitan.

This patch fixes this.
This commit is contained in:
Gabriel Ravier 2023-04-04 20:16:34 +02:00 • committed by GitHub
parent 9c6d78c26d
commit 12e07798df
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3 changed files with 95 additions and 28 deletions
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6
test/libc/fmt/fmt_test.c
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@ -105,10 +105,16 @@ TEST(fmt, o) {
EXPECT_STREQ("0001777777777777777777634", _gc(xasprintf("%#.25lo", -100L)));
EXPECT_STREQ("0001777777777777777777634", _gc(xasprintf("%#.25llo", -100LL)));
EXPECT_STREQ("0", _gc(xasprintf("%#.o", 0)));
EXPECT_STREQ(" 056520", _gc(xasprintf("%#8.6o", 23888)));
EXPECT_STREQ("00144 ", _gc(xasprintf("%#-8.5llo", 100ll)));
EXPECT_STREQ("0 ", _gc(xasprintf("%-#02lo", 0l)));
EXPECT_STREQ("0", _gc(xasprintf("%#01lo", 0l)));
EXPECT_STREQ("00", _gc(xasprintf("%#02lo", 0l)));
}
TEST(fmt, b) {
EXPECT_STREQ("000010100 ", _gc(xasprintf("%-14.9b", 20)));
EXPECT_STREQ("0b110", _gc(xasprintf("%#b", 6)));
}
TEST(fmt, s) {