Merge remote-tracking branch 'upstream/master' into fix_odin_test

2 files changed, 166 insertions, 0 deletions

diff --git a/core/encoding/varint/doc.odin b/core/encoding/varint/doc.odin
new file mode 100644
index 000000000..dd068b261
--- /dev/null
+++ b/core/encoding/varint/doc.odin
@@ -0,0 +1,27 @@
+/*
+	Implementation of the LEB128 variable integer encoding as used by DWARF encoding and DEX files, among others.
+
+	Author of this Odin package: Jeroen van Rijn
+
+	Example:
+		```odin
+		import "core:encoding/varint"
+		import "core:fmt"
+
+		main :: proc() {
+			buf: [varint.LEB128_MAX_BYTES]u8
+
+			value := u128(42)
+
+			encode_size, encode_err := varint.encode_uleb128(buf[:], value)
+			assert(encode_size == 1 && encode_err == .None)
+
+			fmt.println(buf[:encode_size])
+
+			decoded_val, decode_size, decode_err := varint.decode_uleb128(buf[:encode_size])
+			assert(decoded_val == value && decode_size == encode_size && decode_err == .None)
+		}
+		```
+
+*/
+package varint
\ No newline at end of file
diff --git a/core/encoding/varint/leb128.odin b/core/encoding/varint/leb128.odin
new file mode 100644
index 000000000..476b9c2c9
--- /dev/null
+++ b/core/encoding/varint/leb128.odin
@@ -0,0 +1,139 @@
+/*
+	Copyright 2022 Jeroen van Rijn <nom@duclavier.com>.
+	Made available under Odin's BSD-3 license.
+
+	List of contributors:
+		Jeroen van Rijn: Initial implementation.
+*/
+
+// package varint implements variable length integer encoding and decoding using
+// the LEB128 format as used by DWARF debug info, Android .dex and other file formats.
+package varint
+
+import "core:fmt"
+
+// In theory we should use the bigint package. In practice, varints bigger than this indicate a corrupted file.
+// Instead we'll set limits on the values we'll encode/decode
+// 18 * 7 bits = 126, which means that a possible 19th byte may at most be `0b0000_0011`.
+LEB128_MAX_BYTES    :: 19
+
+Error :: enum {
+	None             = 0,
+	Buffer_Too_Small = 1,
+	Value_Too_Large  = 2,
+}
+
+// Decode a slice of bytes encoding an unsigned LEB128 integer into value and number of bytes used.
+// Returns `size` == 0 for an invalid value, empty slice, or a varint > 18 bytes.
+decode_uleb128 :: proc(buf: []u8) -> (val: u128, size: int, err: Error) {
+	more := true
+
+	for v, i in buf {
+		size = i + 1
+
+		// 18 * 7 bits = 126, which means that a possible 19th byte may at most be 0b0000_0011.
+		if size > LEB128_MAX_BYTES || size == LEB128_MAX_BYTES && v > 0b0000_0011 {
+			return 0, 0, .Value_Too_Large
+		}
+
+		val |= u128(v & 0x7f) << uint(i * 7)
+
+		if v < 128 {
+			more = false
+			break
+		}
+	}
+
+	// If the buffer runs out before the number ends, return an error.
+	if more {
+		return 0, 0, .Buffer_Too_Small
+	}
+	return
+}
+
+// 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.
+decode_ileb128 :: proc(buf: []u8) -> (val: i128, size: int, err: Error) {
+	shift: uint
+
+	if len(buf) == 0 {
+		return 0, 0, .Buffer_Too_Small
+	}
+
+	for v in buf {
+		size += 1
+
+		// 18 * 7 bits = 126, which including sign means we can have a 19th byte.
+		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 {
+		val |= max(i128) << shift
+	}
+	return
+}
+
+// Encode `val` into `buf` as an unsigned LEB128 encoded series of bytes.
+// `buf` must be appropriately sized.
+encode_uleb128 :: proc(buf: []u8, val: u128) -> (size: int, err: Error) {
+	val := val
+
+	for {
+		size += 1
+
+		if size > len(buf) {
+			fmt.println(val, buf[:size - 1])
+			return 0, .Buffer_Too_Small
+		}
+
+		low := val & 0x7f
+		val >>= 7
+
+		if val > 0 {
+			low |= 0x80 // more bytes to follow
+		}
+		buf[size - 1] = u8(low)
+
+		if val == 0 { break }
+	}
+	return
+}
+
+@(private)
+SIGN_MASK :: (i128(1) << 121) // sign extend mask
+
+// Encode `val` into `buf` as a signed LEB128 encoded series of bytes.
+// `buf` must be appropriately sized.
+encode_ileb128 :: proc(buf: []u8, val: i128) -> (size: int, err: Error) {
+	val      := val
+	more     := true
+
+	for more {
+		size += 1
+
+		if size > len(buf) {
+			return 0, .Buffer_Too_Small
+		}
+
+		low := val & 0x7f
+		val >>= 7
+
+		low = (low ~ SIGN_MASK) - SIGN_MASK
+
+		if (val == 0 && low & 0x40 != 0x40) || (val == -1 && low & 0x40 == 0x40) {
+			more = false
+		} else {
+			low |= 0x80
+		}
+
+		buf[size - 1] = u8(low)
+	}
+	return
+}
\ No newline at end of file