3 macro_rules! max_leb128_len {
5 // The longest LEB128 encoding for an integer uses 7 bits per byte.
6 (std::mem::size_of::<$int_ty>() * 8 + 6) / 7
10 // Returns the longest LEB128 encoding of all supported integer types.
11 pub const fn max_leb128_len() -> usize {
15 macro_rules! impl_write_unsigned_leb128 {
16 ($fn_name:ident, $int_ty:ty) => {
19 out: &mut [::std::mem::MaybeUninit<u8>; max_leb128_len!($int_ty)],
27 *out.get_unchecked_mut(i).as_mut_ptr() = value as u8;
34 *out.get_unchecked_mut(i).as_mut_ptr() = ((value & 0x7f) | 0x80) as u8;
42 unsafe { ::std::mem::MaybeUninit::slice_assume_init_ref(&out.get_unchecked(..i)) }
47 impl_write_unsigned_leb128!(write_u16_leb128, u16);
48 impl_write_unsigned_leb128!(write_u32_leb128, u32);
49 impl_write_unsigned_leb128!(write_u64_leb128, u64);
50 impl_write_unsigned_leb128!(write_u128_leb128, u128);
51 impl_write_unsigned_leb128!(write_usize_leb128, usize);
53 macro_rules! impl_read_unsigned_leb128 {
54 ($fn_name:ident, $int_ty:ty) => {
56 pub fn $fn_name(slice: &[u8], position: &mut usize) -> $int_ty {
57 // The first iteration of this loop is unpeeled. This is a
58 // performance win because this code is hot and integer values less
59 // than 128 are very common, typically occurring 50-80% or more of
60 // the time, even for u64 and u128.
61 let byte = slice[*position];
63 if (byte & 0x80) == 0 {
64 return byte as $int_ty;
66 let mut result = (byte & 0x7F) as $int_ty;
69 let byte = slice[*position];
71 if (byte & 0x80) == 0 {
72 result |= (byte as $int_ty) << shift;
75 result |= ((byte & 0x7F) as $int_ty) << shift;
83 impl_read_unsigned_leb128!(read_u16_leb128, u16);
84 impl_read_unsigned_leb128!(read_u32_leb128, u32);
85 impl_read_unsigned_leb128!(read_u64_leb128, u64);
86 impl_read_unsigned_leb128!(read_u128_leb128, u128);
87 impl_read_unsigned_leb128!(read_usize_leb128, usize);
89 macro_rules! impl_write_signed_leb128 {
90 ($fn_name:ident, $int_ty:ty) => {
93 out: &mut [::std::mem::MaybeUninit<u8>; max_leb128_len!($int_ty)],
99 let mut byte = (value as u8) & 0x7f;
101 let more = !(((value == 0) && ((byte & 0x40) == 0))
102 || ((value == -1) && ((byte & 0x40) != 0)));
105 byte |= 0x80; // Mark this byte to show that more bytes will follow.
109 *out.get_unchecked_mut(i).as_mut_ptr() = byte;
119 unsafe { ::std::mem::MaybeUninit::slice_assume_init_ref(&out.get_unchecked(..i)) }
124 impl_write_signed_leb128!(write_i16_leb128, i16);
125 impl_write_signed_leb128!(write_i32_leb128, i32);
126 impl_write_signed_leb128!(write_i64_leb128, i64);
127 impl_write_signed_leb128!(write_i128_leb128, i128);
128 impl_write_signed_leb128!(write_isize_leb128, isize);
130 macro_rules! impl_read_signed_leb128 {
131 ($fn_name:ident, $int_ty:ty) => {
133 pub fn $fn_name(slice: &[u8], position: &mut usize) -> $int_ty {
139 byte = slice[*position];
141 result |= <$int_ty>::from(byte & 0x7F) << shift;
144 if (byte & 0x80) == 0 {
149 if (shift < <$int_ty>::BITS) && ((byte & 0x40) != 0) {
151 result |= (!0 << shift);
159 impl_read_signed_leb128!(read_i16_leb128, i16);
160 impl_read_signed_leb128!(read_i32_leb128, i32);
161 impl_read_signed_leb128!(read_i64_leb128, i64);
162 impl_read_signed_leb128!(read_i128_leb128, i128);
163 impl_read_signed_leb128!(read_isize_leb128, isize);