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update png crc handling

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This commit is contained in:
Ryan Oldenburg 2022-06-11 16:10:52 -05:00
parent 7ed8ec507e
commit 97ba8c745f
1 changed files with 14 additions and 11 deletions
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25
src/pixie/fileformats/png.nim
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@ -21,8 +21,8 @@ type
template failInvalid() =
raise newException(PixieError, "Invalid PNG buffer, unable to load")
# template failCRC() =
# raise newException(PixieError, "CRC check failed")
template failCRC() =
raise newException(PixieError, "CRC check failed")
when defined(release):
{.push checks: off.}
@ -400,8 +400,9 @@ proc decodePng*(data: pointer, len: int): Png {.raises: [PixieError].} =
prevChunkType = "IHDR"
inc(pos, 13)
# if crc32(data[pos - 17 ..< pos]) != read32be(data, pos):
# failCRC()
let headerCrc = crc32(data[pos - 17].addr, 17)
if headerCrc != data.readUint32(pos).swap():
failCRC()
inc(pos, 4) # CRC
while true:
@ -462,8 +463,9 @@ proc decodePng*(data: pointer, len: int): Png {.raises: [PixieError].} =
inc(pos, chunkLen)
# if crc32(data[pos - chunkLen - 4 ..< pos]) != read32be(data, pos):
# failCRC()
let chunkCrc = crc32(data[pos - chunkLen - 4].addr, chunkLen + 4)
if chunkCrc != data.readUint32(pos).swap():
failCRC()
inc(pos, 4) # CRC
prevChunkType = chunkType
@ -523,7 +525,7 @@ proc encodePng*(
result.add(0.char)
result.add(0.char)
result.add(0.char)
result.addUint32(crc32(result[result.len - 17 ..< result.len]).swap())
result.addUint32(crc32(result[result.len - 17].addr, 17).swap())
# Add IDAT
# Add room for 1 byte before each row for the filter type.
@ -556,14 +558,15 @@ proc encodePng*(
result.addUint32(compressed.len.uint32.swap())
result.add("IDAT")
result.add(compressed)
result.addUint32(
crc32(result[result.len - compressed.len - 4 ..< result.len]).swap()
)
result.addUint32(crc32(
result[result.len - compressed.len - 4].addr,
compressed.len + 4
).swap())
# Add IEND
result.addUint32(0)
result.add("IEND")
result.addUint32(crc32(result[result.len - 4 ..< result.len]).swap())
result.addUint32(crc32(result[result.len - 4].addr, 4).swap())
proc encodePng*(png: Png): string {.raises: [PixieError].} =
encodePng(png.width, png.height, 4, png.data[0].addr, png.data.len * 4)