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Use memchr for safe and performant read_bytestring #703

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Merged
JonasIsensee merged 1 commit into from
Dec 3, 2025
+8 −8
Merged

Use memchr for safe and performant read_bytestring #703

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
## Unreleased
- Support for directly reading from and writing to Vector{UInt8}
- Fix for working with opened IOStream objects
- Proper boundscheck for internal `read_bytestring`

## 0.6.3
- Fix edge case in datatype loading (#692)
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15 changes: 7 additions & 8 deletions src/io/mmapio.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -201,14 +201,13 @@ end

# Read a null-terminated string
function read_bytestring(io::MmapIO)
# Find the null terminator position without allocating
ptr = pconvert(Ptr{UInt8}, io.curptr)
len = 0
while unsafe_load(ptr, len + 1) != 0x00
len += 1
end
str = len == 0 ? "" : unsafe_string(ptr, len)
io.curptr += len + 1
maxbytes = io.endptr - io.curptr + 1
q = @ccall memchr(ptr::Ptr{UInt8}, 0::Int32, maxbytes::Csize_t)::Ptr{UInt8}
q == C_NULL && throw(EOFError())

str = unsafe_string(ptr, (q - ptr) % Int)
io.curptr += (q - ptr) % Int + 1
str
end

Expand Down Expand Up @@ -239,4 +238,4 @@ function end_checksum(io::MmapIO)
@inbounds v = io.checksum_pos[io.nchecksum]
io.nchecksum -= 1
Lookup3.hash(Ptr{UInt8}(io.startptr + v), position(io) - v)
end
end
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