c - 将 Haskell 中数组的指针传递给 C 函数

Question

我有以下 C 代码:

#include <sys/times.h>
#include <time.h>


float etime_( float *tarray )
{   struct tms buf;

    times( &buf );

    tarray[0] = 1.0 * buf.tms_utime / CLOCKS_PER_SEC;
    tarray[1] = 1.0 * buf.tms_stime / CLOCKS_PER_SEC;

    return tarray[0] + tarray[1];
}

尝试将此 Fortran 代码移植到 Haskell:

  PROGRAM Test
    IMPLICIT NONE

    REAL t, ta(2), etime

    INTEGER i
    DOUBLE PRECISION x

    do i = 1, 10000
       x = sin( cos( i * 1.0 d0 ) )
       print *, x 
    enddo

    ta(1) = 0.0d0
    ta(2) = 0.0d0

    t = etime( ta )       

    PRINT *, 'user time:    ', ta(1)
    PRINT *, 'system time:  ', ta(2)
    PRINT *, 'process time: ', t

  END

如何定义数组和!或者 !!!下面的代码可以工作吗？

module Main where

import GHC.Ptr
import GHC.Prim
import System.IO.Unsafe
import Control.Monad

foreign import ccall etime_ :: Ptr Double → IO Double
etime = etime_

main :: IO Int
main = do
  mapM_ (print . sin . cos . (* (1.0 :: Double)) . fromIntegral) [1..10000 :: Int]
  ta ← array 2
  t ← etime ta
  putStrLn $ "user time:    " ++ show (ta !!! 0)
  putStrLn $ "system time:  " ++ show (ta !!! 1)
  putStrLn $ "process time: " ++ show t
  return 0

array :: Int → IO (Ptr a)
array size = undefined

(!) :: Ptr a → Int → IO a
(!) = undefined

(!!!) :: Ptr a → Int → a
(!!!) = undefined

Answer 1

我建议这样做:

{-# LANGUAGE ForeignFunctionInterface #-}

import Foreign.Marshal.Array (allocaArray, peekArray)
import Foreign.Ptr (Ptr)

foreign import ccall etime_ :: Ptr Float -> IO Float

main :: IO ()
main = do
  mapM_ (print . sin . cos . (* (1.0 :: Double)) . fromIntegral) [1..10000 :: Int]
  allocaArray 2 $ \ta -> do
    ptime <- etime_ ta
    [utime, stime] <- peekArray 2 ta
    putStrLn $ "user time:    " ++ show utime
    putStrLn $ "system time:  " ++ show stime
    putStrLn $ "process time: " ++ show ptime

但要回答您的具体问题:

array :: Storable a => Int -> IO (Ptr a)
array = mallocArray

(!) :: Storable a => Ptr a -> Int -> IO a
(!) = peekElemOff

(!!!) :: Storable a => Ptr a -> Int -> a
(!!!) ptr = unsafePerformIO . peekElemOff ptr

我建议使用hoogle来查找您需要的功能。