Julia代碼優化

Question

我從previous question以下代碼，我需要幫助優化代碼的速度。這是代碼：

function OfdmSym() 
    N = 64 
    n = 1000 
    symbol = ones(Complex{Float64}, n, 64) 
    data = ones(Complex{Float64}, 1, 48) 
    unused = zeros(Complex{Float64}, 1, 12) 
    pilot = ones(Complex{Float64}, 1, 4) 
    s  = [-1-im -1+im 1-im 1+im] 

    for i=1:n     # generate 1000 symbols 
     for j = 1:48   # generate 48 complex data symbols whose basis is s 
       r = rand(1:4) # 1, 2, 3, or 4 
       data[j] = s[r] 
     end 
     symbol[i,:]=[data[1,1:10] pilot[1] data[1,11:20] pilot[2] data[1,21:30] pilot[3] data[1,31:40] pilot[4] data[1,41:48] unused] 
    end 
end 
OfdmSym() 

我感謝您的幫助。

Answer 1

首先，我計時它N = 100000

OfdmSym() # Warmup 
for i = 1:5 
    @time OfdmSym() 
end 

及其相當快，因爲​​它是

elapsed time: 3.235866305 seconds (1278393328 bytes allocated, 15.18% gc time) 
elapsed time: 3.147812323 seconds (1278393328 bytes allocated, 14.89% gc time) 
elapsed time: 3.144739194 seconds (1278393328 bytes allocated, 14.68% gc time) 
elapsed time: 3.118775273 seconds (1278393328 bytes allocated, 14.79% gc time) 
elapsed time: 3.137765971 seconds (1278393328 bytes allocated, 14.85% gc time) 

但我重寫了使用循環，避免切片：

function OfdmSym2() 
    N = 64 
    n = 100000 
    symbol = zeros(Complex{Float64}, n, 64) 
    s  = [-1-im, -1+im, 1-im, 1+im] 
    for i=1:n 
     for j = 1:48 
      @inbounds symbol[i,j] = s[rand(1:4)] 
     end 
     symbol[i,11] = one(Complex{Float64}) 
     symbol[i,22] = one(Complex{Float64}) 
     symbol[i,33] = one(Complex{Float64}) 
     symbol[i,44] = one(Complex{Float64}) 
    end 
end 

OfdmSym2() # Warmup 
for i = 1:5 
    @time OfdmSym2() 
end 

這是快20倍

elapsed time: 0.159715932 seconds (102400256 bytes allocated, 12.80% gc time) 
elapsed time: 0.159113184 seconds (102400256 bytes allocated, 14.75% gc time) 
elapsed time: 0.158200345 seconds (102400256 bytes allocated, 14.82% gc time) 
elapsed time: 0.158469032 seconds (102400256 bytes allocated, 15.00% gc time) 
elapsed time: 0.157919113 seconds (102400256 bytes allocated, 14.86% gc time) 

如果你看一下分析器（@profile），你會看到，大部分的時間都花在生成隨機數，如你所期望的，因爲其他一切都只是走動的數字。

Answer 2

這一切都只是位，對不對？這根本不乾淨（完全不），但它在我的機器上運行速度稍快（這比你的速度慢得多，所以我不會打擾我的時間）。機器上的速度有點快嗎？

function my_OfdmSym() 
    const n = 100000 
    const my_one_bits = uint64(1023) << 52 
    const my_sign_bit = uint64(1) << 63 
    my_sym = Array(Uint64,n<<1,64) 
    fill!(my_sym, my_one_bits) 
    for col = [1:10, 12:21, 23:32, 34:43, 45:52] 
     for row = 1:(n<<1) 
      if randbool() my_sym[row, col] |= my_sign_bit end 
     end 
    end 
    my_symbol = reinterpret(Complex{Float64}, my_sym, (n, 64)) 
    for k in [11, 22, 33, 44] 
     my_symbol[:, k] = 1.0 
    end 
    for k=53:64 
     my_symbol[:, k] = 0.0 
    end 
end