The >=16-significant-digit float-literal-to-php::Decimal promotion
(docs/en/HIGH_PRECISION_TYPES.md) counted every digit in the raw
literal with preg_replace('/[^0-9]/'), so exponent digits and trailing
zeros counted as significant: 1.23456789012345e300 (15 significant
digits) and 999999999999999.0 became Decimal, making
is_float(2.220446049250313E-16) compile to false. Hex literals whose
digits contain E (0x123456789E1234567) matched the [.eE] test and
became Decimal("0x..."), where Zend folds an overflowing hex literal
to its exact double.
Three fixes, keeping the documented feature:
- Count true mantissa significant digits (strip sign, exponent,
leading and trailing zeros) and additionally require that the double
cannot reproduce the literal exactly - a literal that round-trips
(every var_export/serialize output, PHP_FLOAT_EPSILON) has lost
nothing and stays float, while 3.14159265358979323846 still promotes.
- Exclude hex/octal/binary notation from the reclassification.
- When a Decimal-classified literal meets a float-typed expression in
a binary op or comparison, demote the literal to its exact double
instead of the "Cannot convert float expression to Decimal" fatal:
PHP evaluates every float literal as a double, so
0.1 + 0.2 == 0.30000000000000004 is valid PHP and must be true.
Alessio Giacobbe