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Source for wiki BlobAPI version 4

author

cowan

comment

ipnr

198.185.18.207

name

BlobAPI

readonly

text

This is a proposal for a WG2 blob (bytevector) API.  Blobs are a disjoint type.  They have no native interpretation, but parts of them can be interpreted as one of a variety of binary types.  The conceit is that everything is a separate procedure with minimal arguments; this makes for a lot of procedures, but each one can be easily inlined by even a very dumb compiler, providing high efficiency.

=== Basic procedures ===

 `(blob? `''obj''`)`::
  Returns `#t` if ''obj'' is a blob.
 `(make-blob `''n''`)`::
  Returns a newly allocated blob containing ''n'' bytes.
 `(blob-length `''blob''`)`::
  Returns the length of ''blob'' in bytes.
 `(copy-blob `''blob''`)`::
  Returns a newly allocated blob containing the same bytes as ''blob''.
 `(subblob `''blob''` `''from''` `''to''`)`::
  Returns a newly allocated blob containing the bytes in ''blob'' starting at ''start'' (inclusive) and ending at ''end'' (exclusive).
 `(copy-blob! `''from to''`)`::
  Copy blob ''from'' on top of blob ''to'', which must not be shorter.
 `(copy-partial-blob! `''from''` `''start''` `''end''` `''to''` `''at''`)`::
  Copy the part of ''from'' starting at ''start'' and ending at ''end'' into ''to'' starting at ''at''.

Because there is no preferred way to interpret the data in a blob, there is no `blob` function analogous to `list` or `vector` and no second argument to `make-blob`.

=== Numeric procedures ===

 (`blob-<type><endian>-ref` ''blob n''`)`::
  Returns a Scheme number corresponding to the binary value encoded according to ''type'' beginning at offset ''n'' in ''blob''.
 (`blob-<type><endian>-set!` ''blob n v''`)`::
  Converts ''v'' to a binary value encoded according to ''type'' and places it into ''blob'' beginning at offset ''n''.

The types are:

 `u8`::
  unsigned 8-bit integer
 `s8`::
  signed 8-bit integer
 `u16`::
  unsigned 16-bit integer
 `s16`::
  signed 16-bit integer
 `u32`::
  unsigned 32-bit integer
 `s32`::
  signed 32-bit integer
 `u64`::
  unsigned 64-bit integer
 `s64`::
  signed 64-bit integer
 `u128`::
  unsigned 128-bit integer
 `s128`::
  signed 128-bit integer
 `f32`::
  32-bit IEEE float
 `fn32`::
  32-bit native float (may not be IEEE)
 `f64`::
  64-bit IEEE float in native endianism
 `fn64`::
  64-bit native float (may not be IEEE)
 `c64`::
  64-bit complex number (two 32-bit IEEE floats)
 `cn64`::
  64-bit complex number (two 32-bit native floats, may not be IEEE)
 `c128`::
  128-bit complex number (two 64-bit IEEE floats)
 `cn128`::
  128-bit complex number (two 64-bit native floats, may not be IEEE)

The endianism values are:

 (empty)::
  Native endianism (system-dependent)
 `le`::
  Little-endianism
 `be`::
  Big-endianism

Endianism is not applicable to the following types: `s8 u8 fn32 fn64 cn64 cn128`


=== String procedures ===

 (`blob-<encoding>-ref` ''blob n l''`)`::
  Returns a Scheme string corresponding to the binary value encoded according to ''encoding'' beginning at offset ''n'' in ''blob'' and continuing for ''l'' bytes.
 (`blob-<encoding>-set!` ''blob n v''`)`::
  Converts ''v'' to a binary string encoded according to ''encoding'' and places it into ''blob'' beginning at offset ''n''.  Returns the number of bytes encoded.

The encodings are:

 `utf8`::
  UTF-8 encoding
 `utf16`::
  UTF-16 encoding (respects BOM if present, defaults to native encoding otherwise)
 `utf16be`::
  UTF-16BE encoding (treats BOM as a normal character)
 `utf16le`::
  UTF-16LE encoding (treats BOM as a normal character)

=== Issues ===

Pick one:

  1. Offsets are in bytes and can be arbitrary
  1. Offsets are in bytes but must be naturally aligned (divisible by n for an n-byte value)
  1. Offsets are in n-byte sub-blobs (forces natural alignment, SRFI-4 style)

Should `blob=?` be provided?

I've trashed the UTF-32 conversions because nobody uses UTF-32.  They can come back if somebody needs them.

=== WG1 ===

I propose that WG1 provide `blob?, make-blob, blob-length, copy-blob, copy-blob!, blob-u8-ref, blob-u8-set!`, and possibly `subblob` and `copy-partial-blob!` as well.

time

2010-09-23 23:38:02