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Fix 0 before decimal-point in hex float printf fns (#1297)

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The C standard specifies that, upon handling the a conversion specifier,
the argument is converted to a string in which "there is one hexadecimal
digit (which is nonzero [...]) before the decimal-point character", this
being a requirement which cosmopolitan does not currently always handle,
sometimes printing numbers like "0x0.1p+5", where a correct output would
have been e.g. "0x1.0p+1" (despite both representing the same value, the
first one illegally has a '0' digit before the decimal-point character).
This commit is contained in:
Gabriel Ravier 2024-09-16 03:02:47 +02:00 committed by GitHub
parent 81bc8d0963
commit e260d90096
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GPG key ID: B5690EEEBB952194
2 changed files with 20 additions and 11 deletions
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8
libc/stdio/fmt.c
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@ -714,6 +714,7 @@ static int __fmt_bround(struct FPBits *b, int prec, int prec1) {
(b->fpi.rounding == FPI_Round_down && b->sign))
goto inc_true;
// Rounding to nearest, ties to even
if ((t = bits[k >> 3] >> (j = (k & 7) * 4)) & 8) {
if (t & 7)
goto inc_true;
@ -757,7 +758,12 @@ have_inc:
donothing;
if (j > k) {
onebit:
bits[0] = 1;
// We use 0x10 instead of 1 here to ensure that the digit before the
// decimal-point is non-0 (the C standard mandates this, i.e. considers
// that printing 0x0.1p+5 is illegal where 0x1.0p+1 is even though both
// evaluate to the same value because the first has 0 as the digit before
// the decimal-point character)
bits[0] = 0x10;
b->ex += 4 * prec;
return 1;
}

23
test/libc/stdio/snprintf_test.c
View file

@ -233,7 +233,7 @@ void check_a_conversion_specifier_long_double(const char *fmt, const char *expec
ASSERT_STREQ(expected_str, buf);
}
void check_a_conversion_specifier_prec_1(const char *expected_str, double value) {
void check_a_conversion_specifier_double_prec_1(const char *expected_str, double value) {
check_a_conversion_specifier_double("%.1a", expected_str, value);
}
@ -241,10 +241,10 @@ TEST(snprintf, testAConversionSpecifierRounding) {
int previous_rounding = fegetround();
ASSERT_EQ(0, fesetround(FE_DOWNWARD));
check_a_conversion_specifier_prec_1("0x1.fp+4", 0x1.fffffp+4);
check_a_conversion_specifier_double_prec_1("0x1.fp+4", 0x1.fffffp+4);
ASSERT_EQ(0, fesetround(FE_UPWARD));
check_a_conversion_specifier_prec_1("0x2.0p+4", 0x1.f8p+4);
check_a_conversion_specifier_double_prec_1("0x2.0p+4", 0x1.f8p+4);
ASSERT_EQ(0, fesetround(previous_rounding));
}
@ -252,18 +252,21 @@ TEST(snprintf, testAConversionSpecifierRounding) {
// This test specifically checks that we round to even, accordingly to IEEE
// rules
TEST(snprintf, testAConversionSpecifier) {
check_a_conversion_specifier_prec_1("0x1.8p+4", 0x1.7800000000001p+4);
check_a_conversion_specifier_prec_1("0x1.8p+4", 0x1.78p+4);
check_a_conversion_specifier_prec_1("0x1.8p+4", 0x1.88p+4);
check_a_conversion_specifier_prec_1("0x1.6p+4", 0x1.58p+4);
check_a_conversion_specifier_prec_1("0x1.6p+4", 0x1.68p+4);
check_a_conversion_specifier_prec_1("0x1.ap+4", 0x1.98p+4);
check_a_conversion_specifier_prec_1("0x1.ap+4", 0x1.a8p+4);
check_a_conversion_specifier_double_prec_1("0x1.8p+4", 0x1.7800000000001p+4);
check_a_conversion_specifier_double_prec_1("0x1.8p+4", 0x1.78p+4);
check_a_conversion_specifier_double_prec_1("0x1.8p+4", 0x1.88p+4);
check_a_conversion_specifier_double_prec_1("0x1.6p+4", 0x1.58p+4);
check_a_conversion_specifier_double_prec_1("0x1.6p+4", 0x1.68p+4);
check_a_conversion_specifier_double_prec_1("0x1.ap+4", 0x1.98p+4);
check_a_conversion_specifier_double_prec_1("0x1.ap+4", 0x1.a8p+4);
check_a_conversion_specifier_double("%#a", "0x0.p+0", 0x0.0p0);
check_a_conversion_specifier_double("%#A", "0X0.P+0", 0x0.0p0);
check_a_conversion_specifier_long_double("%#La", "0x0.p+0", 0x0.0p0L);
check_a_conversion_specifier_long_double("%#LA", "0X0.P+0", 0x0.0p0L);
check_a_conversion_specifier_double("%.2a", "0x1.00p-1026", 0xf.fffp-1030);
check_a_conversion_specifier_long_double("%.1La", "0x1.0p+1", 1.999L);
}
TEST(snprintf, apostropheFlag) {