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A Common Lisp library for accessing octet-addressed blocks of data
When dealing with network protocols and file formats, it's common to have to read or write 16-, 32-, or 64-bit datatypes in signed or unsigned flavors. Common Lisp sort of supports this by specifying :ELEMENT-TYPE for streams, but that facility is underspecified and there's nothing similar for read/write from octet vectors. What most people wind up doing is rolling their own small facility for their particular needs and calling it a day. This library attempts to be comprehensive and centralize such facilities. Functions to read 16-, 32-, and 64-bit quantities from octet vectors in signed or unsigned flavors are provided; these functions are also SETFable. Since it's sometimes desirable to read/write directly from streams, functions for doing so are also provided. On some implementations, reading/writing IEEE singles/doubles (i.e. SINGLE-FLOAT and DOUBLE-FLOAT) will also be supported. In addition to centralizing such facilities, NIBBLES also aspires to become a place where compiler optimizations can be written once and used everywhere. The intention is that (eventually): (nibbles:sb32ref/le vector index) will compile (with any necessary safety checks) to a MOVSX instruction on an x86oid processor in SBCL (or other implementations) if VECTOR and INDEX are of appropriate types. I remember reading a post on comp.lang.lisp that suggested the designers of Common Lisp ignored the realities of octets and endianness and so forth. This library is a small step towards remedying that deficiency.