Convert a hexadecimal floating point constant from String to BigDecimal.
Since Java 7 the Java language has supported a hexadecimal format for floating point numbers. For example, 0x1p-3 is equal to 0.125; there is a one in the mantissa, and a binary exponent of -3, so it is equal to a one shifted right three places past the binary point, or 3/8.
Similarly, 0xAp-3 is equal to 0xA in the mantissa (0b1010 in binary) shifted right three places. In a hypothetical binary floating point notation we could right this as 1.010 and its values is 1.25. The largest value a double can represent is 0x1.fffffffffffffp1023 (alternatively, this can be written 0x1fffffffffffffp971). That's 53 bits of 1's in the mantissa and the maximum exponent possible.
A double can be created either by writing a literal using this notation in the Java programming language, or by parsing a string in this format with Double::parseDouble.
However, we can easily write values larger than that in this notation, and we can easily work with them in Java using BigDecimal. But at least as of Java 9, BigDecimal doesn't know how to parse a number in this format. You could parse it with Double::parseDouble and then use that to create your BigDecimal, but then you would be restricted to the range of values that double supports.
This project provides a parser that can convert a hexadecimal floating point number that is too large to fit in a double into a BigDecimal.