#9719: Improve `mkInteger` interface -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: task | Status: new Priority: low | Milestone: 7.12.1 Component: Compiler | Version: Resolution: | Keywords: Integer Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Description changed by hvr: Old description:
`mkInteger` is the current operation provided by the `Integer` libraries to construct (large) integer values. The current type-signature is
{{{#!hs mkInteger :: Bool -- sign-bit -> [Int] -- absolute value in 31 bit chunks, least significant first -> Integer }}}
A somewhat pathological example of why this representation is not so nice is the following simple CAF
{{{#!hs c :: Integer c = 0xf000000000000000 }}}
that (this is for a 64bit arch!) gets compiled into the following STG:
{{{ ==================== STG syntax: ==================== sat_sJQ :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [3]; sat_sJR :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJQ GHC.Types.[]]; sat_sJP :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [1610612736]; sat_sJS :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJP sat_sJR]; sat_sJO :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [0]; sat_sJT :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJO sat_sJS]; Foo.c :: GHC.Integer.Type.Integer [GblId, Str=DmdType] = \u srt:SRT:[0Y :-> GHC.Integer.Type.mkInteger, sJT :-> sat_sJT] [] GHC.Integer.Type.mkInteger GHC.Types.True sat_sJT; }}}
Instead a more "natural" `mkInteger` would be desirable, possibly in the style of `unpackCString#`, in terms of a packed/unboxed vector of machine-word-sized chunks. A better `mkInteger` could then take a `ByteArray#` or a `Addr#` + length instead, e.g.
{{{#!hs mkInteger :: Int# -- signum(n) = sign of encoded Integer -- abs(n) = number of machine-word sized chunks -> Addr# -- pointer to start of machine-word sized chunks, -- least-significant chunk first -> Integer }}}
New description: `mkInteger` is the current operation provided by the `Integer` libraries to construct (large) integer values. The current type-signature is {{{#!hs mkInteger :: Bool -- sign-bit -> [Int] -- absolute value in 31 bit chunks, least significant first -> Integer }}} A somewhat pathological example of why this representation is not so nice is the following simple CAF {{{#!hs c :: Integer c = 0xf000000000000000 }}} that (this is for a 64bit arch!) gets compiled into the following STG: {{{ ==================== STG syntax: ==================== sat_sJQ :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [3]; sat_sJR :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJQ GHC.Types.[]]; sat_sJP :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [1610612736]; sat_sJS :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJP sat_sJR]; sat_sJO :: GHC.Types.Int [LclId, Str=DmdType] = NO_CCS GHC.Types.I#! [0]; sat_sJT :: [GHC.Types.Int] [LclId, Str=DmdType] = NO_CCS :! [sat_sJO sat_sJS]; Foo.c :: GHC.Integer.Type.Integer [GblId, Str=DmdType] = \u srt:SRT:[0Y :-> GHC.Integer.Type.mkInteger, sJT :-> sat_sJT] [] GHC.Integer.Type.mkInteger GHC.Types.True sat_sJT; }}} Moreover, determining how much space to allocate for the resulting `Integer` is a bit work as it for one, you need to traverse the list twice, and then you can't simply derive the exact allocation amount by the list-length alone due to the odd 31-bit chunks. Instead a more "natural" `mkInteger` would be desirable, possibly in the style of `unpackCString#`, in terms of a packed/unboxed vector of machine- word-sized chunks. A better `mkInteger` could then take a `ByteArray#` or a `Addr#` + length instead, e.g. {{{#!hs mkInteger :: Int# -- signum(n) = sign of encoded Integer -- abs(n) = number of machine-word sized chunks -> Addr# -- pointer to start of machine-word sized chunks, -- least-significant chunk first -> Integer }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9719#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler