pharpend/Vanillae
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

vdk_binary seems to be done

Browse Source
This commit is contained in:
pharpend
2023-05-25 15:13:16 -06:00
parent ee30eaaf7f
commit a548572de9
14 changed files with 44 additions and 2109 deletions
Download Patch File Download Diff File Expand all files Collapse all files
libs/vdk_binary/src/bin.ts
+417
View File
@@ -0,0 +1,417 @@
/**
* Miscellaneous binary utility functions
*
* @module
*/
export {
// basic bytes functions
bytes_eq,
bytes_concat,
strong_rand_bytes,
bytes_to_bigint,
bigint_to_bytes,
// basic bits functions
bits_null,
bits_zeros,
bits_ones,
bits_i0th,
bits_concat
};
export type {
bits
};
/**
* Bytewise equality of two `Uint8Array`s
*/
function
bytes_eq
(arr1 : Uint8Array,
arr2 : Uint8Array)
: boolean
{
if (arr1.length !== arr2.length)
return false;
else
{
let len : number = arr1.length;
for (let i = 0;
i < len;
i++)
{
if (arr1[i] !== arr2[i])
return false;
}
return true;
}
}
/**
* Concatenate two arrays
*/
function
bytes_concat
(arr1 : Uint8Array,
arr2 : Uint8Array)
: Uint8Array
{
let len1 : number = arr1.length;
let len2 : number = arr2.length;
let arr1_idx0_offset : number = 0;
let arr2_idx0_offset : number = len1;
let result_len : number = len1 + len2;
let result : Uint8Array = new Uint8Array(result_len);
// copy first array into result
for (let arr1_idx0 = 0;
arr1_idx0 < len1;
arr1_idx0++)
{
// no offset here
let result_idx0 : number = arr1_idx0 + arr1_idx0_offset;
result[result_idx0] = arr1[arr1_idx0];
}
// copy second array into result
for (let arr2_idx0 = 0;
arr2_idx0 < len2;
arr2_idx0++)
{
// offset by the length of the first array
let result_idx0 : number = arr2_idx0 + arr2_idx0_offset;
result[result_idx0] = arr2[arr2_idx0];
}
return result;
}
/**
* Cryptographically random bytes
*/
function
strong_rand_bytes
(how_many : number)
: Uint8Array
{
let arr = new Uint8Array(how_many);
(new Crypto()).getRandomValues(arr);
return arr;
}
/**
* Convert a byte array to a bigint
*
* Equivalent to `binary:decode_unsigned/1` from Erlang
*/
function
bytes_to_bigint
(bytes: Uint8Array)
: bigint
{
let n : bigint = 0n;
for (let b of bytes) {
// move first, then add
// otherwise it ends on a move
// imperative languages are for losers
n <<= 8n;
n += BigInt(b);
}
return n;
}
/**
* Convert a bigint to a byte array
*
* Equivalent to `binary:encode_unsigned/1` from Erlang
*
* Requires input to be positive
*/
function
bigint_to_bytes
(q: bigint)
: Uint8Array
{
if (q < 0n) {
throw new Error('q < 0n: ' + q);
}
let arr_reverse = [];
while (q > 0n) {
let r = Number(q % 256n);
q /= 256n;
arr_reverse.push(r);
}
arr_reverse.reverse();
return new Uint8Array(arr_reverse);
}
/**
* Oh no, bitstrings in a language that only has bytestrings
*
* By convention these are `Uint8Array`s with byte length `ceil(bit_length /
* 8)`, and all trailing bits are zero.
*/
type bits =
{bit_length : number,
bytes : Uint8Array};
/**
* Get an uninitialized bitstring
*
* @internal
*/
function
bits_null
(bit_length : number)
: bits
{
let byte_length : number = Math.ceil(bit_length / 8);
let result : Uint8Array = new Uint8Array(byte_length);
return {bit_length : bit_length,
bytes : result};
}
/**
* Get a bitstring of a given length where every value is 0.
*/
function
bits_zeros
(bit_length : number)
: bits
{
let byte_length : number = Math.ceil(bit_length / 8);
let result : Uint8Array = new Uint8Array(byte_length);
for (let i0 = 0;
i0 < byte_length;
i0++)
{
result[i0] = 0;
}
return {bit_length : bit_length,
bytes : result};
}
/**
* Get a bitstring of a given length where every value is 1.
*/
function
bits_ones
(bit_length : number)
: bits
{
let byte_length : number = Math.ceil(bit_length / 8);
let result : Uint8Array = new Uint8Array(byte_length);
// fill everything except the last byte with 255s
for (let i0 = 0;
i0 < (byte_length - 1);
i0++)
{
result[i0] = 255;
}
// alright so the last byte
// ok so the number of leading 0s is
// 8 - (bit_length % 8)
let num_trailing_zero_bits : number = 8 - (bit_length % 8);
// the trailing byte is 255 << that
// e.g. 3 trailing 0s
// 1111_1111 -> 1111_1000
let last_byte : number = 255 << num_trailing_zero_bits;
let last_byte_idx0 : number = byte_length - 1;
result[last_byte_idx0] = last_byte;
return {bit_length : bit_length,
bytes : result};
}
/**
* Get the bit at a given 0-index
*/
function
bits_i0th
(bit_idx0 : number,
bits : bits)
: number
{
// first task is figuring out what byte we're at
// for instance if we want bit 27
// 3*8 = 24 =< 27 < 4*8
// so it's Math.floor(bit_idx0 / 8)
let byte_idx0 : number = Math.floor(bit_idx0 / 8);
// let's fetch the byte and work with that
let the_byte : number = bits.bytes[byte_idx0];
// ok so let's go with 27 again
// 27 = 3 mod 8
// so we bitshift right by (8 - 3)
// and then take the remainder dividing by 2
// --B-_---- -> ----_---B -> 0000_000B
let bsr : number = 8 - (bit_idx0 % 8);
return (the_byte >> bsr) % 2;
}
/**
* Concatenate two bitstrings
*/
function
bits_concat
(bits1 : bits,
bits2 : bits)
: bits
{
let result_bit_length : number = bits1.bit_length + bits2.bit_length;
let bytes1 : Uint8Array = bits1.bytes;
let bytes2 : Uint8Array = bits2.bytes;
// using zeros here because of our xor trick in a minute
let result_bits : bits = bits_null(result_bit_length);
let result_bytes : Uint8Array = result_bits.bytes;
// go along each byte in result, and compute the byte boundary
for (let i = 0;
i < result_bytes.length;
i++)
{
// ABCD_EFGH _
// 0123_4567 8
// this is the bit index of the leftmost bit in this byte
let start_bit_bi0 : number = i * 8;
let next_start_bit_bi0 : number = start_bit_bi0 + 8;
// does the bit at the beginning of this byte correspond to the first array?
// strict comparison:
// suppose i = 0,
// suppose bit_length1 is 0
// then this says no, go to second array
// suppose bl1 = 1,
// this says start at first array
let start_bit_is_of_first_array : boolean = start_bit_bi0 < bits1.bit_length;
// weak comparison:
// suppose bit_length1 = 8
// ABCD_EFGH _
// 0123_4567 8
// ^
// start_bit_bi0 ^ next_start_bit_bi0
let stop_bit_is_of_first_array : boolean = next_start_bit_bi0 <= bits1.bit_length;
// is this a bytes1 byte
let is_bytes1_byte : boolean = start_bit_is_of_first_array && stop_bit_is_of_first_array;
let is_boundary_byte : boolean = start_bit_is_of_first_array && !stop_bit_is_of_first_array;
// need to work out the ping_pong bs up here because js is dumb and I
// can't put lets between elseifs
// alright, now we're in the case of only copying from the second array
// we have two cases:
// ping-pong:
// ABCD_EFGH 1234_5678
// - ---- ---
// copying these bits
// ping:
// ABCD_EFGH <end>
// - ---- 000
//
// how to distinguish between these two??
//
// we're in the ping case when the start_bit_bi0 corresponds to the
// final byte of the second array
//
// ok
//
// we need to compute the bit address in the second array that
// corresponds to the bit address at the beginning of this byte in the
// result array
let bits2_addr_bi0 : number = start_bit_bi0 - bits1.bit_length;
// I think the variable is
// bits_left_to_copy = bits2.bit_length - bit_addr2_bi0
// no + 1 because the current bit is uncopied,
// so if bit_addr2_bi0 = 7 and bits2.bit_length is 8, it means we
// have the last bit to copy
// cases:
// bits_left_to_copy <= 0 ->
// this would mean we have more bits to copy, but are out of
// source bits. should be impossible if bits_null is correct
// bits_left_to_copy <= 8 ->
// this would mean we are going to fill this last byte in the
// result array with the correct bits from array2, but how we
// do this will depend on how those are arranged in bytes2
// (whether we grab one or two bytes)
//
// this is the tricky case
//
// I think what matters here is the byte address in the second array
// if we're on the last byte
// 8 < bits_left_to_copy ->
// this means we can safely grab two bytes from bytes2, and do
// our bitshifting to make it correct
//
// FIXME
let bits_left_to_copy : number = bits2.bit_length - bits2_addr_bi0;
// no the variable that matters is which byte we're on in the result
let this_bytes2_addr_i0 : number = Math.floor(bits2_addr_bi0 / 8);
let next_bytes2_addr_i0 : number = this_bytes2_addr_i0 + 1;
let bitshift_amt : number = bits1.bit_length % 8;
let ping : boolean = next_bytes2_addr_i0 === bytes2.length;
// simple case: this is a byte from the first array
// just copy it
if (is_bytes1_byte)
result_bytes[i] = bytes1[i];
// this is a boundary byte
// further cases:
// second bit length is 0 ->
// ABCD_EF-- <empty>
// ^ starting here
// just copy first byte and move along
else if (is_boundary_byte && (bits2.bit_length === 0))
result_bytes[i] = bytes1[i];
// boundary byte, and there is at least one byte in the second array
else if (is_boundary_byte)
{
// copy over the first byte
result_bytes[i] = bytes1[i];
// take the first byte from the second array
let first_byte_of_second_array : number = bytes2[0];
// bytes1:
// ABCD_EF00
// 6
// bytes2:
// 1234_5678
// 0000_0012
// and bitshift it right by that amount
let bitshift_amt : number = bits1.bit_length % 8;
result_bytes[i] ^= first_byte_of_second_array >> bitshift_amt;
}
// last byte of second array
else if (ping)
result_bytes[i] = (bytes2[this_bytes2_addr_i0] << bitshift_amt);
// ping-pong: not last byte of second array
else
result_bytes[i] = (bytes2[this_bytes2_addr_i0] << bitshift_amt) ^ (bytes2[next_bytes2_addr_i0] << bitshift_amt);
}
return {bit_length : result_bit_length,
bytes : result_bytes};
}