clean up and export crc32c function (#22274)

* clean up and export crc32c function

* added PR to NEWS

* restore crc32 of String, add crc32c(io) to read all of a stream, add optimized open(crc32c, filename), make IOBuffer checksums consistent with other streams

* use crc32c block size of 8192*3, matching the underling C library

* optimized IOBuffer crc32c

Author: stevengj

NEWS.md

@@ -59,6 +59,8 @@ Library improvements
   * `resize!` and `sizehint!` methods no longer over-reserve memory when the
     requested array size is more than double of its current size ([#22038]).
 
+  * The `crc32c` function for CRC-32c checksums is now exported ([#22274]).
+
   * The output of `versioninfo()` is now controlled with keyword arguments ([#21974]).
 
   * The function `LibGit2.set_remote_url` now always sets both the fetch and push URLs for a

base/exports.jl

@@ -1047,6 +1047,7 @@ export
     atexit,
     atreplinit,
     clipboard,
+    crc32c,
     exit,
     ntuple,
     quit,

base/iobuffer.jl

@@ -412,3 +412,15 @@ function readuntil(io::AbstractIOBuffer, delim::UInt8)
     end
     A
 end
+
+# copy-free crc32c of IOBuffer:
+function crc32c(io::IOBuffer, nb::Integer, crc::UInt32=0x00000000)
+    nb < 0 && throw(ArgumentError("number of bytes to checksum must be ≥ 0"))
+    io.readable || throw(ArgumentError("read failed, IOBuffer is not readable"))
+    n = min(nb, nb_available(io))
+    n == 0 && return crc
+    crc = unsafe_crc32c(pointer(io.data, io.ptr), n, crc)
+    io.ptr += n
+    return crc
+end
+crc32c(io::IOBuffer, crc::UInt32=0x00000000) = crc32c(io, nb_available(io), crc)

base/loading.jl

@@ -683,10 +683,7 @@ function compilecache(name::String)
     if success(create_expr_cache(path, cachefile, concrete_deps))
         # append checksum to the end of the .ji file:
         open(cachefile, "a+") do f
-            data = Mmap.mmap(f, Vector{UInt8}, filesize(f), 0)
-            checksum = crc32c(data)
-            finalize(data)
-            write(f, hton(checksum))
+            write(f, hton(crc32c(seekstart(f))))
         end
     else
         error("Failed to precompile $name to $cachefile.")
@@ -809,12 +806,8 @@ function stale_cachefile(modpath::String, cachefile::String)
         end
 
         # finally, verify that the cache file has a valid checksum
-        data = Mmap.mmap(io, Vector{UInt8}, filesize(io), 0)
-        # checksum = UInt32 read in bigendian format from the last 4 bytes:
-        checksum = UInt32(data[end]) + UInt32(data[end-1])<<8 + UInt32(data[end-2])<<16 + UInt32(data[end-3])<<24
-        crc = crc32c(@view(data[1:end-4]))
-        finalize(data)
-        if checksum != crc
+        crc = crc32c(seekstart(io), filesize(io)-4)
+        if crc != ntoh(read(io, UInt32))
             DEBUG_LOADING[] && info("JL_DEBUG_LOADING: Rejecting cache file $cachefile because it has an invalid checksum.")
             return true
         end

base/util.jl

@@ -765,10 +765,6 @@ if is_windows()
 
 end
 
-# compute sizeof correctly for strings, arrays, and subarrays of bytes
-_sizeof(a) = sizeof(a)
-_sizeof(a::FastContiguousSubArray{UInt8,N,<:Array{UInt8}} where N) = length(a)
-
 """
     crc32c(data, crc::UInt32=0x00000000)
 
@@ -778,9 +774,49 @@ a starting `crc` integer to be mixed in with the checksum.  The `crc` parameter
 can be used to compute a checksum on data divided into chunks: performing
 `crc32c(data2, crc32c(data1))` is equivalent to the checksum of `[data1; data2]`.
 (Technically, a little-endian checksum is computed.)
+
+There is also a method `crc32c(io, nb, crc)` to checksum `nb` bytes from
+a stream `io`, or `crc32c(io, crc)` to checksum all the remaining bytes.
+Hence you can do [`open(crc32c, filename)`](@ref) to checksum an entire file,
+or `crc32c(seekstart(buf))` to checksum an [`IOBuffer`](@ref) without
+calling [`take!`](@ref).
+
+For a `String`, note that the result is specific to the UTF-8 encoding
+(a different checksum would be obtained from a different Unicode encoding).
+To checksum an `a::Array` of some other bitstype, you can do `crc32c(reinterpret(UInt8,a))`,
+but note that the result may be endian-dependent.
 """
-crc32c(a::Union{Array{UInt8},FastContiguousSubArray{UInt8,N,<:Array{UInt8}} where N,String}, crc::UInt32=0x00000000) =
-    ccall(:jl_crc32c, UInt32, (UInt32, Ptr{UInt8}, Csize_t), crc, a, _sizeof(a))
+function crc32c end
+
+unsafe_crc32c(a, n, crc) = ccall(:jl_crc32c, UInt32, (UInt32, Ptr{UInt8}, Csize_t), crc, a, n)
+
+crc32c(a::Union{Array{UInt8},FastContiguousSubArray{UInt8,N,<:Array{UInt8}} where N}, crc::UInt32=0x00000000) =
+    unsafe_crc32c(a, length(a), crc)
+
+crc32c(s::String, crc::UInt32=0x00000000) = unsafe_crc32c(s, sizeof(s), crc)
+
+"""
+    crc32c(io::IO, [nb::Integer,] crc::UInt32=0x00000000)
+
+Read up to `nb` bytes from `io` and return the CRC-32c checksum, optionally
+mixed with a starting `crc` integer.  If `nb` is not supplied, then
+`io` will be read until the end of the stream.
+"""
+function crc32c(io::IO, nb::Integer, crc::UInt32=0x00000000)
+    nb < 0 && throw(ArgumentError("number of bytes to checksum must be ≥ 0"))
+    # use block size 24576=8192*3, since that is the threshold for
+    # 3-way parallel SIMD code in the underlying jl_crc32c C function.
+    buf = Array{UInt8}(min(nb, 24576))
+    while !eof(io) && nb > 24576
+        n = readbytes!(io, buf)
+        crc = unsafe_crc32c(buf, n, crc)
+        nb -= n
+    end
+    return unsafe_crc32c(buf, readbytes!(io, buf, min(nb, length(buf))), crc)
+end
+crc32c(io::IO, crc::UInt32=0x00000000) = crc32c(io, typemax(Int64), crc)
+crc32c(io::IOStream, crc::UInt32=0x00000000) = crc32c(io, filesize(io)-position(io), crc)
+
 
 """
     @kwdef typedef

doc/src/stdlib/arrays.md

@@ -131,6 +131,7 @@ Base.cumprod!
 Base.cumsum
 Base.cumsum!
 Base.cumsum_kbn
+Base.crc32c
 Base.LinAlg.diff
 Base.LinAlg.gradient
 Base.rot180

doc/src/stdlib/io-network.md

@@ -12,6 +12,7 @@ Base.take!(::Base.AbstractIOBuffer)
 Base.fdio
 Base.flush
 Base.close
+Base.crc32c(::IO, ::Integer, ::UInt32)
 Base.write
 Base.read
 Base.read!

test/misc.jl

@@ -566,14 +566,42 @@ end
 for force_software_crc in (1,0)
     ccall(:jl_crc32c_init, Void, (Cint,), force_software_crc)
     for (n,crc) in [(0,0x00000000),(1,0xa016d052),(2,0x03f89f52),(3,0xf130f21e),(4,0x29308cf4),(5,0x53518fab),(6,0x4f4dfbab),(7,0xbd3a64dc),(8,0x46891f81),(9,0x5a14b9f9),(10,0xb219db69),(11,0xd232a91f),(12,0x51a15563),(13,0x9f92de41),(14,0x4d8ae017),(15,0xc8b74611),(16,0xa0de6714),(17,0x672c992a),(18,0xe8206eb6),(19,0xc52fd285),(20,0x327b0397),(21,0x318263dd),(22,0x08485ccd),(23,0xea44d29e),(24,0xf6c0cb13),(25,0x3969bba2),(26,0x6a8810ec),(27,0x75b3d0df),(28,0x82d535b1),(29,0xbdf7fc12),(30,0x1f836b7d),(31,0xd29f33af),(32,0x8e4acb3e),(33,0x1cbee2d1),(34,0xb25f7132),(35,0xb0fa484c),(36,0xb9d262b4),(37,0x3207fe27),(38,0xa024d7ac),(39,0x49a2e7c5),(40,0x0e2c157f),(41,0x25f7427f),(42,0x368c6adc),(43,0x75efd4a5),(44,0xa84c5c31),(45,0x0fc817b2),(46,0x8d99a881),(47,0x5cc3c078),(48,0x9983d5e2),(49,0x9267c2db),(50,0xc96d4745),(51,0x058d8df3),(52,0x453f9cf3),(53,0xb714ade1),(54,0x55d3c2bc),(55,0x495710d0),(56,0x3bddf494),(57,0x4f2577d0),(58,0xdae0f604),(59,0x3c57c632),(60,0xfe39bbb0),(61,0x6f5d1d41),(62,0x7d996665),(63,0x68c738dc),(64,0x8dfea7ae)]
-        @test Base.crc32c(UInt8[1:n;]) == crc
+        @test crc32c(UInt8[1:n;]) == crc == crc32c(String(UInt8[1:n;]))
     end
     # test that crc parameter is equivalent to checksum of concatenated data,
     # and test crc of subarrays:
     a = UInt8[1:255;]
-    crc_256 = Base.crc32c(UInt8[1:255;])
+    crc_256 = crc32c(a)
     @views for n = 1:255
-        @test Base.crc32c(a[n+1:end], Base.crc32c(a[1:n])) == crc_256
+        @test crc32c(a[n+1:end], crc32c(a[1:n])) == crc_256
+    end
+
+    @test crc32c(IOBuffer(a)) == crc_256
+    let buf = IOBuffer()
+        write(buf, a[1:3])
+        @test crc32c(seekstart(buf)) == crc32c(a[1:3])
+        @test crc32c(buf) == 0x00000000
+        @test crc32c(seek(buf, 1)) == crc32c(a[2:3])
+        @test crc32c(seek(buf, 0), 2) == crc32c(a[1:2])
+        @test crc32c(buf) == crc32c(a[3:3])
+    end
+
+    let f = tempname()
+        try
+            write(f, a)
+            @test open(crc32c, f) == crc_256
+            open(f, "r") do io
+                @test crc32c(io, 16) == crc32c(a[1:16])
+                @test crc32c(io, 16) == crc32c(a[17:32])
+                @test crc32c(io) == crc32c(a[33:end])
+                @test crc32c(io, 1000) == 0x00000000
+            end
+            a = rand(UInt8, 30000)
+            write(f, a)
+            @test open(crc32c, f) == crc32c(a) == open(io -> crc32c(io, 10^6), f)
+        finally
+            rm(f, force=true)
+        end
     end
 end