Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | 16x 16x 16x 2494x 2494x 2494x 24940x 2494x 168x 168x 2016x 168x | import type { ErrorCorrectionLevel } from "../types";
import { EC_FORMAT_BITS } from "./capacity";
/**
* Format and version information, both protected by BCH codes
* (ISO/IEC 18004 §7.9 and §7.10).
*
* These 15- and 18-bit words are what a scanner reads *first*, before it knows
* anything else about the symbol, so they carry their own error correction and
* — for the format word — an XOR mask that guarantees the field is never all
* zeroes (which would be indistinguishable from a blank region).
*/
/** BCH(15,5) generator for the format information. */
const FORMAT_GENERATOR = 0x537;
/** The constant the format bits are XORed with so they're never all zero. */
const FORMAT_MASK = 0x5412;
/** BCH(18,6) generator for the version information. */
const VERSION_GENERATOR = 0x1f25;
/**
* The 15-bit format word for an EC level and mask pattern, BCH-protected and
* masked.
*/
export function formatInfoBits(level: ErrorCorrectionLevel, mask: number): number {
const data = (EC_FORMAT_BITS[level] << 3) | mask;
let remainder = data;
for (let i = 0; i < 10; i++) {
remainder = (remainder << 1) ^ ((remainder >>> 9) * FORMAT_GENERATOR);
}
return (((data << 10) | remainder) ^ FORMAT_MASK) & 0x7fff;
}
/**
* The 18-bit version word, BCH-protected. Only versions 7 and up carry one —
* smaller symbols are identified by their module count alone.
*/
export function versionInfoBits(version: number): number {
let remainder = version;
for (let i = 0; i < 12; i++) {
remainder = (remainder << 1) ^ ((remainder >>> 11) * VERSION_GENERATOR);
}
return ((version << 12) | remainder) & 0x3ffff;
}
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