luaur_vm/functions/
buffer_writebits.rs

1use luaur_common::macros::luau_big_endian::LUAU_BIG_ENDIAN;
2
3use crate::functions::lua_l_checkbuffer::lua_l_checkbuffer;
4use crate::functions::lua_l_checkinteger::lua_l_checkinteger;
5use crate::functions::lua_l_checknumber::lua_l_checknumber;
6use crate::functions::lua_l_checkunsigned::lua_l_checkunsigned;
7use crate::macros::lua_l_error::luaL_error;
8use crate::type_aliases::lua_state::lua_State;
9
10pub fn buffer_writebits(L: *mut lua_State) -> core::ffi::c_int {
11    let mut len: usize = 0;
12    let buf = lua_l_checkbuffer(L, 1, &mut len) as *mut core::ffi::c_char;
13    let bitoffset = lua_l_checknumber(L, 2) as i64;
14    let bitcount = lua_l_checkinteger(L, 3);
15    let value = lua_l_checkunsigned(L, 4);
16
17    if bitoffset < 0 {
18        unsafe {
19            luaL_error!(L, "buffer access out of bounds");
20        }
21    }
22
23    if bitcount < 0 || bitcount > 32 {
24        unsafe {
25            luaL_error!(L, "bit count is out of range of [0; 32]");
26        }
27    }
28
29    if (bitoffset as u64 + bitcount as u64) > (len as u64) * 8 {
30        unsafe {
31            luaL_error!(L, "buffer access out of bounds");
32        }
33    }
34
35    let startbyte = (bitoffset / 8) as usize;
36    let endbyte = ((bitoffset + bitcount as i64 + 7) / 8) as usize;
37
38    let mut data: u64 = 0;
39
40    if LUAU_BIG_ENDIAN {
41        for i in (startbyte..endbyte).rev() {
42            data = data * 256 + (unsafe { *buf.add(i) } as u8) as u64;
43        }
44    } else {
45        unsafe {
46            core::ptr::copy_nonoverlapping(
47                buf.add(startbyte),
48                &mut data as *mut u64 as *mut core::ffi::c_char,
49                endbyte - startbyte,
50            );
51        }
52    }
53
54    let subbyteoffset = (bitoffset & 0x7) as u64;
55    let mask = (((1u64 << bitcount) - 1) << subbyteoffset) as u64;
56
57    data = (data & !mask) | (((value as u64) << subbyteoffset) & mask);
58
59    if LUAU_BIG_ENDIAN {
60        for i in startbyte..endbyte {
61            unsafe {
62                *buf.add(i) = (data & 0xff) as core::ffi::c_char;
63            }
64            data >>= 8;
65        }
66    } else {
67        unsafe {
68            core::ptr::copy_nonoverlapping(
69                &data as *const u64 as *const core::ffi::c_char,
70                buf.add(startbyte),
71                endbyte - startbyte,
72            );
73        }
74    }
75
76    0
77}
luaur_vm/functions/buffer_writebits.rs

luaur_vm/functions/
buffer_writebits.rs
