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Merge pull request #1722 from Kelimion/varint_streamed

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[LEB128] Add byte-at-a-time ILEB decoder.
This commit is contained in:
Jeroen van Rijn
2022-04-16 18:19:38 +02:00
committed by GitHub
parent b6f3fa6ee1 6d0ba8d189
commit 70cbffd58b
1 changed files with 29 additions and 15 deletions
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core/encoding/varint/leb128.odin
+29 -15
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@@ -66,33 +66,47 @@ decode_uleb128 :: proc {decode_uleb128_buffer, decode_uleb128_byte}
// Decode a slice of bytes encoding a signed LEB128 integer into value and number of bytes used. // Decode a slice of bytes encoding a signed LEB128 integer into value and number of bytes used.
// Returns `size` == 0 for an invalid value, empty slice, or a varint > 18 bytes. // Returns `size` == 0 for an invalid value, empty slice, or a varint > 18 bytes.
decode_ileb128 :: proc(buf: []u8) -> (val: i128, size: int, err: Error) { decode_ileb128_buffer :: proc(buf: []u8) -> (val: i128, size: int, err: Error) {
shift: uint
if len(buf) == 0 { if len(buf) == 0 {
return 0, 0, .Buffer_Too_Small return 0, 0, .Buffer_Too_Small
} }
for v in buf { for v in buf {
size += 1 val, size, err = decode_ileb128_byte(v, size, val)
if err != .Buffer_Too_Small {
// 18 * 7 bits = 126, which including sign means we can have a 19th byte. return
if size > LEB128_MAX_BYTES || size == LEB128_MAX_BYTES && v > 0x7f {
return 0, 0, .Value_Too_Large
} }
val |= i128(v & 0x7f) << shift
shift += 7
if v < 128 { break }
} }
if buf[size - 1] & 0x40 == 0x40 { if err == .Buffer_Too_Small {
val |= max(i128) << shift val, size = 0, 0
} }
return return
} }
// Decode a a signed LEB128 integer into value and number of bytes used, one byte at a time.
// Returns `size` == 0 for an invalid value, empty slice, or a varint > 18 bytes.
decode_ileb128_byte :: proc(input: u8, offset: int, accumulator: i128) -> (val: i128, size: int, err: Error) {
size = offset + 1
shift := uint(offset * 7)
// 18 * 7 bits = 126, which including sign means we can have a 19th byte.
if size > LEB128_MAX_BYTES || size == LEB128_MAX_BYTES && input > 0x7f {
return 0, 0, .Value_Too_Large
}
val = accumulator | i128(input & 0x7f) << shift
if input < 128 {
if input & 0x40 == 0x40 {
val |= max(i128) << (shift + 7)
}
return val, size, .None
}
return val, size, .Buffer_Too_Small
}
decode_ileb128 :: proc{decode_ileb128_buffer, decode_ileb128_byte}
// Encode `val` into `buf` as an unsigned LEB128 encoded series of bytes. // Encode `val` into `buf` as an unsigned LEB128 encoded series of bytes.
// `buf` must be appropriately sized. // `buf` must be appropriately sized.
encode_uleb128 :: proc(buf: []u8, val: u128) -> (size: int, err: Error) { encode_uleb128 :: proc(buf: []u8, val: u128) -> (size: int, err: Error) {