/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
âvi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :viâ
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â Copyright 2021 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
â                                                                              â
â THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                â
â WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                â
â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
â DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        â
â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
â TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             â
â PERFORMANCE OF THIS SOFTWARE.                                                â
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ*/
#include "libc/intrin/bits.h"
#include "libc/zip.h"

typedef char v16qi __attribute__((__vector_size__(16)));
typedef short v8hi __attribute__((__vector_size__(16)));
typedef long long v2di __attribute__((__vector_size__(16), __aligned__(1)));

/**
 * Locates End Of Central Directory record in ZIP file.
 *
 * The ZIP spec says this header can be anywhere in the last 64kb. We
 * search it backwards for the ZIP-64 "PKâ â¢" magic number. If that's not
 * found, then we search again for the original "PKâ£â " magnum. The
 * caller needs to check the first four bytes of the returned value to
 * determine whether to use ZIP_CDIR_xxx() or ZIP_CDIR64_xxx() macros.
 *
 * @param p points to file memory
 * @param n is byte size of file
 * @return pointer to EOCD64 or EOCD, or NULL if not found
 */
void *GetZipCdir(const uint8_t *p, size_t n) {
  v2di x;
  size_t i, j;
  uint32_t magic;
  i = n - 4;
  do {
#ifdef __x86_64__
    v8hi pk = {READ16LE("PK"), READ16LE("PK"), READ16LE("PK"), READ16LE("PK"),
               READ16LE("PK"), READ16LE("PK"), READ16LE("PK"), READ16LE("PK")};
    asm("" : "+x"(pk));
    if (i >= 14) {
      x = *(const v2di *)(p + i - 14);
      if (!(__builtin_ia32_pmovmskb128(
                (v16qi)__builtin_ia32_pcmpeqw128((v8hi)x, pk)) |
            __builtin_ia32_pmovmskb128((v16qi)__builtin_ia32_pcmpeqw128(
                (v8hi)__builtin_ia32_psrldqi128(x, 8), pk)))) {
        i -= 13;
        continue;
      }
    }
#endif
    while (magic = READ32LE(p + i), magic != kZipCdir64LocatorMagic &&
                                        magic != kZipCdirHdrMagic &&
                                        i + 0x10000 + 0x1000 >= n && i > 0) {
      --i;
    }
    if (magic == kZipCdir64LocatorMagic && i + kZipCdir64LocatorSize <= n &&
        IsZipCdir64(p, n, ZIP_LOCATE64_OFFSET(p + i))) {
      return p + ZIP_LOCATE64_OFFSET(p + i);
    } else if (magic == kZipCdirHdrMagic && IsZipCdir32(p, n, i)) {
      j = i;
      do {
        if (READ32LE(p + j) == kZipCdir64LocatorMagic &&
            j + kZipCdir64LocatorSize <= n &&
            IsZipCdir64(p, n, ZIP_LOCATE64_OFFSET(p + j))) {
          return p + ZIP_LOCATE64_OFFSET(p + j);
        }
      } while (j-- && i - j < 128);
      return p + i;
    }
  } while (i > 0 && i-- + 0x10000 + 0x1000 >= n);
  return 0;
}
