Fix ascii and utf8 and some ccall usage

[yuyichao]

1. Make sure utf8, ascii and bytestring always check if the pointer is NULL.
2. Avoid useless copy and dynamic dispatch in ascii and utf8.
3. Fix some out-of-date ccall usage to reduce avoid a few type assertions.

[yuyichao]

..... Does @github not support force pushing to update a pull request anymore??

[timholy]

I'm having trouble over in #13323, too.

[Keno]

https://status.github.com/messages

[yuyichao]

thx, looks good now =)

[yuyichao]

Using the micro benchmarks here

using Benchmarks

function show_benchmark_result(r)
    stats = Benchmarks.SummaryStatistics(r)
    max_length = 24
    if isnull(stats.elapsed_time_lower) || isnull(stats.elapsed_time_upper)
        @printf("%s: %s\n",
                Benchmarks.lpad("Time per evaluation", max_length),
                Benchmarks.pretty_time_string(stats.elapsed_time_center))
    else
        @printf("%s: %s [%s, %s]\n",
                Benchmarks.lpad("Time per evaluation", max_length),
                Benchmarks.pretty_time_string(stats.elapsed_time_center),
                Benchmarks.pretty_time_string(get(stats.elapsed_time_lower)),
                Benchmarks.pretty_time_string(get(stats.elapsed_time_upper)))
    end
end

macro show_benchmark(ex)
    quote
        println($(QuoteNode(ex)))
        show_benchmark_result(@benchmark $(esc(ex)))
    end
end

ascii_strs = ["0123"^i for i in (1, 10, 100, 1000)]
utf8_strs = ["αβγδ"^i for i in (1, 10, 100, 1000)]

println("ASCII:")
for s in ascii_strs
    sp = pointer(s)
    print(length(s), " ")
    @show_benchmark utf8(sp)
    print(length(s), " ")
    @show_benchmark utf8(sp, 4)
    print(length(s), " ")
    @show_benchmark ascii(sp)
    print(length(s), " ")
    @show_benchmark ascii(sp, 4)
end

println("UTF8:")
for s in utf8_strs
    sp = pointer(s)
    print(length(s), " ")
    @show_benchmark utf8(sp)
    print(length(s), " ")
    @show_benchmark utf8(sp, 8)
end

Here's the difference in the performance...

--- old 2016-04-06 19:13:39.020357001 -0400
+++ new 2016-04-06 19:12:30.263410217 -0400
@@ -1,50 +1,50 @@
 ASCII:
 4 utf8(sp)
-     Time per evaluation: 161.08 ns [157.90 ns, 164.25 ns]
+     Time per evaluation: 82.06 ns [80.48 ns, 83.65 ns]
 4 utf8(sp,4)
-     Time per evaluation: 201.50 ns [197.38 ns, 205.62 ns]
+     Time per evaluation: 84.34 ns [82.71 ns, 85.96 ns]
 4 ascii(sp)
-     Time per evaluation: 142.29 ns [139.31 ns, 145.28 ns]
+     Time per evaluation: 90.84 ns [88.94 ns, 92.73 ns]
 4 ascii(sp,4)
-     Time per evaluation: 85.85 ns [84.11 ns, 87.58 ns]
+     Time per evaluation: 89.44 ns [87.61 ns, 91.27 ns]
 40 utf8(sp)
-     Time per evaluation: 197.29 ns [193.21 ns, 201.38 ns]
+     Time per evaluation: 115.88 ns [113.91 ns, 117.84 ns]
 40 utf8(sp,4)
-     Time per evaluation: 186.16 ns [182.02 ns, 190.31 ns]
+     Time per evaluation: 89.39 ns [87.50 ns, 91.27 ns]
 40 ascii(sp)
-     Time per evaluation: 172.80 ns [168.85 ns, 176.75 ns]
+     Time per evaluation: 133.23 ns [130.67 ns, 135.79 ns]
 40 ascii(sp,4)
-     Time per evaluation: 87.99 ns [86.20 ns, 89.77 ns]
+     Time per evaluation: 86.12 ns [84.42 ns, 87.81 ns]
 400 utf8(sp)
-     Time per evaluation: 470.00 ns [459.50 ns, 480.51 ns]
+     Time per evaluation: 252.85 ns [247.65 ns, 258.05 ns]
 400 utf8(sp,4)
-     Time per evaluation: 199.70 ns [195.20 ns, 204.20 ns]
+     Time per evaluation: 84.45 ns [82.80 ns, 86.10 ns]
 400 ascii(sp)
-     Time per evaluation: 462.67 ns [452.84 ns, 472.50 ns]
+     Time per evaluation: 410.02 ns [400.55 ns, 419.49 ns]
 400 ascii(sp,4)
-     Time per evaluation: 91.41 ns [89.50 ns, 93.31 ns]
+     Time per evaluation: 87.52 ns [85.93 ns, 89.11 ns]
 4000 utf8(sp)
-     Time per evaluation: 2.18 μs [2.13 μs, 2.23 μs]
+     Time per evaluation: 848.01 ns [836.11 ns, 859.91 ns]
 4000 utf8(sp,4)
-     Time per evaluation: 197.69 ns [193.64 ns, 201.74 ns]
+     Time per evaluation: 82.98 ns [81.42 ns, 84.53 ns]
 4000 ascii(sp)
-     Time per evaluation: 2.10 μs [2.05 μs, 2.15 μs]
+     Time per evaluation: 2.08 μs [2.03 μs, 2.13 μs]
 4000 ascii(sp,4)
-     Time per evaluation: 88.43 ns [86.73 ns, 90.13 ns]
+     Time per evaluation: 84.14 ns [82.55 ns, 85.73 ns]
 UTF8:
 4 utf8(sp)
-     Time per evaluation: 163.07 ns [159.61 ns, 166.53 ns]
+     Time per evaluation: 83.08 ns [81.48 ns, 84.67 ns]
 4 utf8(sp,8)
-     Time per evaluation: 199.50 ns [195.06 ns, 203.93 ns]
+     Time per evaluation: 80.24 ns [78.65 ns, 81.84 ns]
 40 utf8(sp)
-     Time per evaluation: 259.66 ns [254.55 ns, 264.78 ns]
+     Time per evaluation: 130.54 ns [128.34 ns, 132.74 ns]
 40 utf8(sp,8)
-     Time per evaluation: 193.80 ns [189.88 ns, 197.72 ns]
+     Time per evaluation: 82.75 ns [81.10 ns, 84.41 ns]
 400 utf8(sp)
-     Time per evaluation: 996.22 ns [970.59 ns, 1.02 μs]
+     Time per evaluation: 361.85 ns [354.73 ns, 368.96 ns]
 400 utf8(sp,8)
-     Time per evaluation: 201.93 ns [197.81 ns, 206.05 ns]
+     Time per evaluation: 82.45 ns [80.74 ns, 84.17 ns]
 4000 utf8(sp)
-     Time per evaluation: 6.87 μs [6.66 μs, 7.08 μs]
+     Time per evaluation: 1.17 μs [1.15 μs, 1.19 μs]
 4000 utf8(sp,8)
-     Time per evaluation: 205.73 ns [201.35 ns, 210.12 ns]
+     Time per evaluation: 77.77 ns [76.27 ns, 79.27 ns]