Since Schemes may support unlimited size bignums it is useful to support the binary encoding of such values.
A BER (Basic Encoding Rules from X.690) compressed integer is an unsigned integer in base 128, most significant digit first, where the high bit is set on all but the final (least significant) byte. Thus any size integer can be encoded, but the encoding is efficient and small integers don't take up any more space than they would in normal char/short/int encodings. This is commonly used to encode an unlimited length field, and can form the basis for other variable length encodings.
Examples of integers converted to BER byte sequences:
3 => #x03
555 => #x84 #x2B
123456789 => #xBA #xEF #x9A #x15
This will become a modified BER encoder plus a schema-based C struct converter.
The default value of port is the current input or output port, as appropriate.
It is an error if the ports passed to these procedures are not binary ports.
Procedure names with @ are used as an abbreviation for different numeric
types: see SRFI 160 for
the full list.
(read-@ [port])
Reads the appropriate number of bytes from port in native byte order and returns a number of the appropriate type (exact integer or inexact real or complex number).
(read-@le [port])
Reads the appropriate number of bytes from port in little-endian byte order and returns a number of the appropriate type (exact integer or inexact real or complex number).
(read-@be [port])
Reads the appropriate number of bytes from port in big-endian ("network") byte order and returns a number of the appropriate type (exact integer or inexact real or complex number).
(write-@ number [port])
Writes number to port in the appropriate format using native byte order.
(write-@le number [port])
Writes number to port in the appropriate format using little-endian byte order.
(write-@be number [port])
Writes number to port in the appropriate format using big-endian ("network") byte order.
(read-ber-integer [port])
Reads a BER-encoded integer of arbitrary size from port and returns it as an exact integer.
(write-ber-integer exact-integer [port])
Writes exact-integer using BER encoding to port. It is an error if exact-integer is negative.
ber-integer-size int
Return the number of bytes required to encode int in BER format.
bytevector-ber-integer-ref bytevector k
Reads and returns an exact integer starting at offset k in bytevector.
bytevector-ber-integer-set! bytevector k exact-integer
Writes the exact integer exact-integer to bytevector in BER format starting at offset k It is an error if exact-integer is negative.
(read-utf8-string k [port])
Read k bytes from port, interpreting them as a sequence of characters encoded in UTF-8, and return the sequence as a string. It is an error if the implementation forbids any of the characters in strings, except that if the implementation forbids null characters in strings and the final character is a null, then it is discarded.
(write-utf8-string string [port])
Convert the characters of string to UTF-8
and write the bytes to port.
(read-bytevector-until byte [port])
Read bytes from port until a byte equal to byte is read. Return two values: all the other bytes as a bytevector, and byte.
See SRFI 56 for implementation.