[GHC] #11143: Feature request: Add index/read/write primops with byte offset for ByteArray#

28 Nov 2015

      #11143: Feature request: Add index/read/write primops with byte offset for
ByteArray#
-------------------------------------+-------------------------------------
           Reporter:  vagarenko      |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Currently, primops for indexing `ByteArray#` and reading/writing
 `MutableByteArray#` have the following form:
 {{{#!hs
 indexTYPEArray# :: ByteArray#          -> Int# -> TYPE#
 readTYPEArray#  :: MutableByteArray# s -> Int# -> State# s -> (#State# s,
 TYPE##)
 writeTYPEArray# :: MutableByteArray# s -> Int# -> TYPE# -> State# s ->
 State# s
 }}}
 where second argument of type `Int#` is an offset measured in terms of the
 size of `TYPE#`.

 This is inconvinient if I want to store values of different types inside
 `ByteArray#`: I have to read values of type `Int8` and then glue them
 together with some bitwise operations.

 I suggest adding number of primops, similar to existing ones, which would
 accept offset in bytes from the start of the `ByteArray#`:
 {{{#!hs
 -- | Read 8-bit integer; offset in bytes.
 indexByteInt8Array#  :: ByteArray# -> Int# -> Int#

 -- | Read 16-bit integer; offset in bytes.
 indexByteInt16Array# :: ByteArray# -> Int# -> Int#

 -- | Read 32-bit integer; offset in bytes.
 indexByteInt32Array# :: ByteArray# -> Int# -> Int#

 -- | Read 8-bit integer; offset in bytes.
 readInt8Array#  :: MutableByteArray# s -> Int# -> State# s -> (#State# s,
 Int##)

 -- | Read 16-bit integer; offset in bytes.
 readInt16Array# :: MutableByteArray# s -> Int# -> State# s -> (#State# s,
 Int##)

 -- | Read 32-bit integer; offset in bytes.
 readInt32Array# :: MutableByteArray# s -> Int# -> State# s -> (#State# s,
 Int##)
 }}}
 and so on...

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11143
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler