export function memcpy(dest: usize, src: usize, n: usize): void { // see: musl/src/string/memcpy.c
  let w: u32, x: u32;

  // copy 1 byte each until src is aligned to 4 bytes
  while (n && (src & 3)) {
    store<u8>(dest++, load<u8>(src++));
    n--;
  }

  // if dst is aligned to 4 bytes as well, copy 4 bytes each
  if ((dest & 3) == 0) {
    while (n >= 16) {
      store<u32>(dest     , load<u32>(src     ));
      store<u32>(dest +  4, load<u32>(src +  4));
      store<u32>(dest +  8, load<u32>(src +  8));
      store<u32>(dest + 12, load<u32>(src + 12));
      src += 16; dest += 16; n -= 16;
    }
    if (n & 8) {
      store<u32>(dest    , load<u32>(src    ));
      store<u32>(dest + 4, load<u32>(src + 4));
      dest += 8; src += 8;
    }
    if (n & 4) {
      store<u32>(dest, load<u32>(src));
      dest += 4; src += 4;
    }
    if (n & 2) { // drop to 2 bytes each
      store<u16>(dest, load<u16>(src));
      dest += 2; src += 2;
    }
    if (n & 1) { // drop to 1 byte
      store<u8>(dest++, load<u8>(src++));
    }
    return;
  }

  // if dst is not aligned to 4 bytes, use alternating shifts to copy 4 bytes each
  // doing shifts if faster when copying enough bytes (here: 32 or more)
  if (n >= 32) {
    switch (<u32>dest & 3) {
      // known to be != 0
      case 1: {
        w = load<u32>(src);
        store<u8>(dest++, load<u8>(src++));
        store<u8>(dest++, load<u8>(src++));
        store<u8>(dest++, load<u8>(src++));
        n -= 3;
        while (n >= 17) {
          x = load<u32>(src + 1);
          store<u32>(dest, w >> 24 | x << 8);
          w = load<u32>(src + 5);
          store<u32>(dest + 4, x >> 24 | w << 8);
          x = load<u32>(src + 9);
          store<u32>(dest + 8, w >> 24 | x << 8);
          w = load<u32>(src + 13);
          store<u32>(dest + 12, x >> 24 | w << 8);
          src += 16; dest += 16; n -= 16;
        }
        break;
      }
      case 2: {
        w = load<u32>(src);
        store<u8>(dest++, load<u8>(src++));
        store<u8>(dest++, load<u8>(src++));
        n -= 2;
        while (n >= 18) {
          x = load<u32>(src + 2);
          store<u32>(dest, w >> 16 | x << 16);
          w = load<u32>(src + 6);
          store<u32>(dest + 4, x >> 16 | w << 16);
          x = load<u32>(src + 10);
          store<u32>(dest + 8, w >> 16 | x << 16);
          w = load<u32>(src + 14);
          store<u32>(dest + 12, x >> 16 | w << 16);
          src += 16; dest += 16; n -= 16;
        }
        break;
      }
      case 3: {
        w = load<u32>(src);
        store<u8>(dest++, load<u8>(src++));
        n -= 1;
        while (n >= 19) {
          x = load<u32>(src + 3);
          store<u32>(dest, w >> 8 | x << 24);
          w = load<u32>(src + 7);
          store<u32>(dest + 4, x >> 8 | w << 24);
          x = load<u32>(src + 11);
          store<u32>(dest + 8, w >> 8 | x << 24);
          w = load<u32>(src + 15);
          store<u32>(dest + 12, x >> 8 | w << 24);
          src += 16; dest += 16; n -= 16;
        }
        break;
      }
    }
  }

  // copy remaining bytes one by one
  if (n & 16) {
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
  }
  if (n & 8) {
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
  }
  if (n & 4) {
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
  }
  if (n & 2) {
    store<u8>(dest++, load<u8>(src++));
    store<u8>(dest++, load<u8>(src++));
  }
  if (n & 1) {
    store<u8>(dest++, load<u8>(src++));
  }
}

// @ts-ignore: decorator
@inline
export function memmove(dest: usize, src: usize, n: usize): void { // see: musl/src/string/memmove.c
  if (dest == src) return;
  if (ASC_SHRINK_LEVEL < 1) {
    if (src - dest - n <= -(n << 1)) {
      memcpy(dest, src, n);
      return;
    }
  }
  if (dest < src) {
    if (ASC_SHRINK_LEVEL < 2) {
      if ((src & 7) == (dest & 7)) {
        while (dest & 7) {
          if (!n) return;
          --n;
          store<u8>(dest++, load<u8>(src++));
        }
        while (n >= 8) {
          store<u64>(dest, load<u64>(src));
          n    -= 8;
          dest += 8;
          src  += 8;
        }
      }
    }
    while (n) {
      store<u8>(dest++, load<u8>(src++));
      --n;
    }
  } else {
    if (ASC_SHRINK_LEVEL < 2) {
      if ((src & 7) == (dest & 7)) {
        while ((dest + n) & 7) {
          if (!n) return;
          store<u8>(dest + --n, load<u8>(src + n));
        }
        while (n >= 8) {
          n -= 8;
          store<u64>(dest + n, load<u64>(src + n));
        }
      }
    }
    while (n) {
      store<u8>(dest + --n, load<u8>(src + n));
    }
  }
}

// @ts-ignore: decorator
@inline
export function memset(dest: usize, c: u8, n: usize): void { // see: musl/src/string/memset
  if (ASC_SHRINK_LEVEL > 1) {
    while (n) {
      store<u8>(dest++, c);
      --n;
    }
  } else {
    // fill head and tail with minimal branching
    if (!n) return;
    let dend = dest + n;
    store<u8>(dest, c);
    store<u8>(dend - 1, c);
    if (n <= 2) return;
    store<u8>(dest, c, 1);
    store<u8>(dest, c, 2);
    store<u8>(dend - 2, c);
    store<u8>(dend - 3, c);
    if (n <= 6) return;
    store<u8>(dest, c, 3);
    store<u8>(dend - 4, c);
    if (n <= 8) return;

    // advance pointer to align it at 4-byte boundary
    let k: usize = -dest & 3;
    dest += k;
    n -= k;
    n &= -4;

    let c32: u32 = <u32>-1 / 255 * c;

    // fill head/tail up to 28 bytes each in preparation
    dend = dest + n;
    store<u32>(dest, c32);
    store<u32>(dend - 4, c32);
    if (n <= 8) return;
    store<u32>(dest, c32, 4);
    store<u32>(dest, c32, 8);
    store<u32>(dend - 12, c32);
    store<u32>(dend - 8, c32);
    if (n <= 24) return;
    store<u32>(dest, c32, 12);
    store<u32>(dest, c32, 16);
    store<u32>(dest, c32, 20);
    store<u32>(dest, c32, 24);
    store<u32>(dend - 28, c32);
    store<u32>(dend - 24, c32);
    store<u32>(dend - 20, c32);
    store<u32>(dend - 16, c32);

    // align to a multiple of 8
    k = 24 + (dest & 4);
    dest += k;
    n -= k;

    // copy 32 bytes each
    let c64: u64 = <u64>c32 | (<u64>c32 << 32);
    while (n >= 32) {
      store<u64>(dest, c64);
      store<u64>(dest, c64, 8);
      store<u64>(dest, c64, 16);
      store<u64>(dest, c64, 24);
      n -= 32;
      dest += 32;
    }
  }
}

// @ts-ignore: decorator
@inline
export function memcmp(vl: usize, vr: usize, n: usize): i32 {
  if (vl == vr) return 0;
  if (ASC_SHRINK_LEVEL < 2) {
    if ((vl & 7) == (vr & 7)) {
      while (vl & 7) {
        if (!n) return 0;
        let a = <i32>load<u8>(vl);
        let b = <i32>load<u8>(vr);
        if (a != b) return a - b;
        n--; vl++; vr++;
      }
      while (n >= 8) {
        if (load<u64>(vl) != load<u64>(vr)) break;
        vl += 8;
        vr += 8;
        n  -= 8;
      }
    }
  }
  while (n--) {
    let a = <i32>load<u8>(vl);
    let b = <i32>load<u8>(vr);
    if (a != b) return a - b;
    vl++; vr++;
  }
  return 0;
}
