tf2-rtp-calculator/src/hash.ts

An RTP calculator for Team Fortress 2 crate unbox sessions

/**
 * Hashing functions for a TF2 unbox.
 * Hashes and unhashes into a 32-bit integer.
 */

/* ----- bit positions & masks ----- */

const HAT_SHIFT   = 0,  HAT_MASK   = 0xff << HAT_SHIFT;
const STR_SHIFT   = 8,  STR_MASK   = 1    << STR_SHIFT;
const UNUS_SHIFT  = 9,  UNUS_MASK  = 1    << UNUS_SHIFT;
const FX_SHIFT    = 10, FX_MASK    = 0xff << FX_SHIFT;

/* ----- types/interfaces ----- */

interface HatFlags {
  hatIndex:            number; // 0-255
  isStrange:           0 | 1;
  isUnusual:           0 | 1;
  unusualEffectIndex?: number; // 0-255 when isUnusual === 1
}

/* ----- functions ----- */

/**
 * Hashes the given hat flags into a 32-bit integer.
 * @param hatIndex The index of the hat inside the crate.
 * @param isStrange 1 if strange, 0 if not strange.
 * @param isUnusual 1 if unusual, 0 if not unusual.
 * @param unusualEffectIndex The index of the unusual effect inside the crate.
 */
export function hash(
  hatIndex: number,
  isStrange: 0 | 1,
  isUnusual: 0 | 1,
  unusualEffectIndex: number,
): number {
  let v =
    ((hatIndex & 0xff)       << HAT_SHIFT)  |
    ((isStrange & 1)         << STR_SHIFT)  |
    ((isUnusual & 1)         << UNUS_SHIFT) |
    ((unusualEffectIndex & 0xff) << FX_SHIFT);

  return v >>> 0;               // force Uint32
}

/**
 * Unhashes the given 32-bit integer into hat flags.
 * @param v The hashed value to unhash.
 */
export function unhash(v: number): HatFlags {
  const hatIndex  =  (v & HAT_MASK)  >>> HAT_SHIFT;
  const isStrange = ((v & STR_MASK)  >>> STR_SHIFT) as 0 | 1;
  const isUnusual = ((v & UNUS_MASK) >>> UNUS_SHIFT) as 0 | 1;

  const flags: HatFlags = { hatIndex, isStrange, isUnusual };
  flags.unusualEffectIndex = (v & FX_MASK) >>> FX_SHIFT;
  return flags;
}