US-ASCII character support.
The following functions act only on US-ASCII code points, that is on the bytes in range [0x00;0x7F]. The functions can be safely used on UTF-8 encoded strings, they will of course only deal with US-ASCII related matters.
References.
is_digit c is true iff c is an US-ASCII digit '0' ... '9', that is a byte in the range [0x30;0x39].
is_hex_digit c is true iff c is an US-ASCII hexadecimal digit '0' ... '9', 'a' ... 'f', 'A' ... 'F', that is a byte in one of the ranges [0x30;0x39], [0x41;0x46], [0x61;0x66].
hex_digit_value c is the numerical value of a digit that satisfies is_hex_digit. Raises Invalid_argument if is_hex_digit c is false.
lower_hex_digit n is an hexadecimal digit for the integer n truncated to its lowest 4 bits.
upper_hex_digit n is an hexadecimal digit for the integer n truncated to its lowest 4 bits.
is_valid c is true iff c is an US-ASCII character, that is a byte in the range [0x00;0x7F].
is_upper c is true iff c is an US-ASCII uppercase letter 'A' ... 'Z', that is a byte in the range [0x41;0x5A].
is_lower c is true iff c is an US-ASCII lowercase letter 'a' ... 'z', that is a byte in the range [0x61;0x7A].
is_white c is true iff c is an US-ASCII white space character, that is one of space ' ' (0x20), tab '\t' (0x09), newline '\n' (0x0A), vertical tab (0x0B), form feed (0x0C), carriage return '\r' (0x0D).
is_blank c is true iff c is an US-ASCII blank character, that is either space ' ' (0x20) or tab '\t' (0x09).
is_graphic c is true iff c is an US-ASCII graphic character that is a byte in the range [0x21;0x7E].
is_control c is true iff c is an US-ASCII control character, that is a byte in the range [0x00;0x1F] or 0x7F.
uppercase c is c with US-ASCII characters 'a' to 'z' mapped to 'A' to 'Z'.