image-size
Version:
get dimensions of any image file
42 lines (40 loc) • 1.31 kB
JavaScript
// lib/utils/bit-reader.ts
var BitReader = class {
constructor(input, endianness) {
this.input = input;
this.endianness = endianness;
// Skip the first 16 bits (2 bytes) of signature
this.byteOffset = 2;
this.bitOffset = 0;
}
/** Reads a specified number of bits, and move the offset */
getBits(length = 1) {
let result = 0;
let bitsRead = 0;
while (bitsRead < length) {
if (this.byteOffset >= this.input.length) {
throw new Error("Reached end of input");
}
const currentByte = this.input[this.byteOffset];
const bitsLeft = 8 - this.bitOffset;
const bitsToRead = Math.min(length - bitsRead, bitsLeft);
if (this.endianness === "little-endian") {
const mask = (1 << bitsToRead) - 1;
const bits = currentByte >> this.bitOffset & mask;
result |= bits << bitsRead;
} else {
const mask = (1 << bitsToRead) - 1 << 8 - this.bitOffset - bitsToRead;
const bits = (currentByte & mask) >> 8 - this.bitOffset - bitsToRead;
result = result << bitsToRead | bits;
}
bitsRead += bitsToRead;
this.bitOffset += bitsToRead;
if (this.bitOffset === 8) {
this.byteOffset++;
this.bitOffset = 0;
}
}
return result;
}
};
export { BitReader };