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String: Fix default decimals truncation in num and num_real 

Fixes undefined behavior, and fixes the logic for negative powers of ten.
Fixes #51764.

Adds tests to validate the changes and prevent regressions.
Adds docs for `String.num`.
This commit is contained in:
Rémi Verschelde 2021-08-17 11:43:11 +02:00
parent c4e03672e8
commit 066dbc2f0c
No known key found for this signature in database
GPG Key ID: C3336907360768E1
3 changed files with 59 additions and 7 deletions
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27
core/string/ustring.cpp
View File

@ -1396,7 +1396,13 @@ String String::num(double p_num, int p_decimals) {
#ifndef NO_USE_STDLIB
if (p_decimals < 0) {
p_decimals = 14 - (int)floor(log10(p_num));
p_decimals = 14;
const double abs_num = ABS(p_num);
if (abs_num > 10) {
// We want to align the digits to the above sane default, so we only
// need to subtract log10 for numbers with a positive power of ten.
p_decimals -= (int)floor(log10(abs_num));
}
}
if (p_decimals > MAX_DECIMALS) {
p_decimals = MAX_DECIMALS;
@ -1625,24 +1631,31 @@ String String::num_real(double p_num, bool p_trailing) {
String s;
String sd;
/* integer part */
// Integer part.
bool neg = p_num < 0;
p_num = ABS(p_num);
int intn = (int)p_num;
/* decimal part */
// Decimal part.
if ((int)p_num != p_num) {
double dec = p_num - (double)((int)p_num);
if (intn != p_num) {
double dec = p_num - (double)(intn);
int digit = 0;
#if REAL_T_IS_DOUBLE
int decimals = 14 - (int)floor(log10(p_num));
int decimals = 14;
#else
int decimals = 6 - (int)floor(log10(p_num));
int decimals = 6;
#endif
// We want to align the digits to the above sane default, so we only
// need to subtract log10 for numbers with a positive power of ten.
if (p_num > 10) {
decimals -= (int)floor(log10(p_num));
}
if (decimals > MAX_DECIMALS) {
decimals = MAX_DECIMALS;
}

15
doc/classes/String.xml
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@ -410,6 +410,21 @@
<argument index="0" name="number" type="float" />
<argument index="1" name="decimals" type="int" default="-1" />
<description>
Converts a [float] to a string representation of a decimal number.
The number of decimal places can be specified with [code]decimals[/code]. If [code]decimals[/code] is [code]-1[/code] (default), decimal places will be automatically adjusted so that the string representation has 14 significant digits (counting both digits to the left and the right of the decimal point).
Trailing zeros are not included in the string. The last digit will be rounded and not truncated.
Some examples:
[codeblock]
String.num(3.141593) # "3.141593"
String.num(3.141593, 3) # "3.142"
String.num(3.14159300) # "3.141593", no trailing zeros.
# Last digit will be rounded up here, which reduces total digit count since
# trailing zeros are removed:
String.num(42.129999, 5) # "42.13"
# If `decimals` is not specified, the total amount of significant digits is 14:
String.num(-0.0000012345432123454321) # "-0.00000123454321"
String.num(-10000.0000012345432123454321) # "-10000.0000012345"
[/codeblock]
</description>
</method>
<method name="num_scientific" qualifiers="static">

24
tests/test_string.h
View File

@ -350,6 +350,9 @@ TEST_CASE("[String] Insertion") {
}
TEST_CASE("[String] Number to string") {
CHECK(String::num(0) == "0");
CHECK(String::num(0.0) == "0"); // No trailing zeros.
CHECK(String::num(-0.0) == "-0"); // Includes sign even for zero.
CHECK(String::num(3.141593) == "3.141593");
CHECK(String::num(3.141593, 3) == "3.142");
CHECK(String::num_real(3.141593) == "3.141593");
@ -357,6 +360,27 @@ TEST_CASE("[String] Number to string") {
CHECK(String::num_int64(3141593) == "3141593");
CHECK(String::num_int64(0xA141593, 16) == "a141593");
CHECK(String::num_int64(0xA141593, 16, true) == "A141593");
CHECK(String::num(42.100023, 4) == "42.1"); // No trailing zeros.
// Checks doubles with many decimal places.
CHECK(String::num(0.0000012345432123454321, -1) == "0.00000123454321"); // -1 uses 14 as sane default.
CHECK(String::num(0.0000012345432123454321) == "0.00000123454321"); // -1 is the default value.
CHECK(String::num(-0.0000012345432123454321) == "-0.00000123454321");
CHECK(String::num(-10000.0000012345432123454321) == "-10000.0000012345");
CHECK(String::num(0.0000000000012345432123454321) == "0.00000000000123");
CHECK(String::num(0.0000000000012345432123454321, 3) == "0");
// Note: When relevant (remainder > 0.5), the last digit gets rounded up,
// which can also lead to not include a trailing zero, e.g. "...89" -> "...9".
CHECK(String::num(0.0000056789876567898765) == "0.00000567898766"); // Should round last digit.
CHECK(String::num(10000.000005678999999999) == "10000.000005679"); // We cut at ...789|99 which is rounded to ...79, so only 13 decimals.
CHECK(String::num(42.12999999, 6) == "42.13"); // Also happens with lower decimals count.
// 32 is MAX_DECIMALS. We can't reliably store that many so we can't compare against a string,
// but we can check that the string length is 34 (32 + 2 for "0.").
CHECK(String::num(0.00000123456789987654321123456789987654321, 32).length() == 34);
CHECK(String::num(0.00000123456789987654321123456789987654321, 42).length() == 34); // Should enforce MAX_DECIMALS.
CHECK(String::num(10000.00000123456789987654321123456789987654321, 42).length() == 38); // 32 decimals + "10000.".
}
TEST_CASE("[String] String to integer") {