The Standard ML Basis Library

The PACK_WORD signature

The Pack{N}Big and Pack{N}Little structures provide facilities for packing and unpacking N-bit word elements into Word8 vectors. The Pack{N}Big structures perform big-endian packing and unpacking, and the Pack{N}Little structures perform little-endian packing and unpacking. In a big-endian system, the word order is high-byte/low-byte; in a little-endian system, it is low-byte/high-byte.

Synopsis

signature PACK_WORD
structure Pack{N}Big : PACK_WORD
structure Pack{N}Little : PACK_WORD


Interface

val bytesPerElem : int
val isBigEndian : bool
val subVec : (Word8Vector.vector * int) -> LargeWord.word
val subVecX : (Word8Vector.vector * int) -> LargeWord.word
val subArr : (Word8Array.array * int) -> LargeWord.word
val subArrX : (Word8Array.array * int) -> LargeWord.word
val update : (Word8Array.array * int * LargeWord.word) -> unit


Description

bytesPerElem

is the number of bytes per element. Most implementations will provide several structures with values of bytesPerElem that are small powers of two (e.g., 1, 2, 4, and 8, corresponding to N of 8, 16, 32, 64, respectively).

isBigEndian

is true if the structure implements a big-endian view of the data.

subVec (vec, i)

subVecX (vec, i)

extracts the subvector vec[bytesPerElem*i .. bytesPerElem*i+bytesPerElem-1] of the vector vec and converts it into a word according to the endianess of the structure. The subVecX version extends the sign bit (most significant bit) when converting the subvector to a word. Raise exception Subscript if i < 0, or if (Word8Vector.length(vec) / bytesPerElem) <= i.

subArr (arr, i)

subArrX (arr, i)

extracts the subvector arr[bytesPerElem*i .. bytesPerElem*i+bytesPerElem-1] of the array arr and converts it into a word according to the endianess of the structure. The subArrX version extends the sign bit (most significant bit) when converting the subarray into a word. Raises exception Subscript if i < 0 or if (Word8Array.length(arr) / bytesPerElem) <= i.

update (arr, i, j)

stores the bytesPerElem low-order bytes of the word w into the bytes bytesPerElem*i through bytesPerElem*(i+1)-1 of the array arr, according to the structure's endianess. Raises exception Subscript if i < 0 or if (Word8Array.length(arr) / bytesPerElem) <= i.

See Also

Byte, MONO_ARRAY, MONO_VECTOR, LargeWord

Last Modified January 9, 1997
Copyright © 1996 AT&T