This is xnu-8019. See this file in:
#include <sys/cdefs.h>
#include "WKdm.h"

/***************************************************************************
 *          THE UNPACKING ROUTINES should GO HERE
 */

const char hashLookupTable[] = HASH_LOOKUP_TABLE_CONTENTS;

#if 0
#define GET_NEXT_TAG tags[tagsIndex++]
#define GET_NEXT_FULL_PATTERN fullPatterns[fullPatternsIndex++]
#define GET_NEXT_LOW_BITS lowBits[lowBitsIndex++]
#define GET_NEXT_DICTIONARY_INDEX dictionaryIndices[dictionaryIndicesIndex++]
#endif

/*  WK_unpack_2bits takes any number of words containing 16 two-bit values
 *  and unpacks them into four times as many words containg those
 *  two bit values as bytes (with the low two bits of each byte holding
 *  the actual value.
 */
static WK_word*
WK_unpack_2bits(WK_word *input_buf,
    WK_word *input_end,
    WK_word *output_buf)
{
	WK_word *input_next = input_buf;
	WK_word *output_next = output_buf;
	WK_word packing_mask = TWO_BITS_PACKING_MASK;

	/* loop to repeatedly grab one input word and unpack it into
	 * 4 output words.  This loop could be unrolled a little---it's
	 * designed to be easy to do that.
	 */
	while (input_next < input_end) {
		WK_word temp = input_next[0];
		DEBUG_PRINT_2("Unpacked tags word: %.8x\n", temp);
		output_next[0] = temp & packing_mask;
		output_next[1] = (temp >> 2) & packing_mask;
		output_next[2] = (temp >> 4) & packing_mask;
		output_next[3] = (temp >> 6) & packing_mask;

		output_next += 4;
		input_next++;
	}

	return output_next;
}

/* unpack four bits consumes any number of words (between input_buf
 * and input_end) holding 8 4-bit values per word, and unpacks them
 * into twice as many words, with each value in a separate byte.
 * (The four-bit values occupy the low halves of the bytes in the
 * result).
 */
static WK_word*
WK_unpack_4bits(WK_word *input_buf,
    WK_word *input_end,
    WK_word *output_buf)
{
	WK_word *input_next = input_buf;
	WK_word *output_next = output_buf;
	WK_word packing_mask = FOUR_BITS_PACKING_MASK;


	/* loop to repeatedly grab one input word and unpack it into
	 * 4 output words.  This loop should probably be unrolled
	 * a little---it's designed to be easy to do that.
	 */
	while (input_next < input_end) {
		WK_word temp = input_next[0];
		DEBUG_PRINT_2("Unpacked dictionary indices word: %.8x\n", temp);
		output_next[0] = temp & packing_mask;
		output_next[1] = (temp >> 4) & packing_mask;

		output_next += 2;
		input_next++;
	}

	return output_next;
}

/* unpack_3_tenbits unpacks three 10-bit items from (the low 30 bits of)
 * a 32-bit word
 */
static WK_word*
WK_unpack_3_tenbits(WK_word *input_buf,
    WK_word *input_end,
    WK_word *output_buf)
{
	WK_word *input_next = input_buf;
	WK_word *output_next = output_buf;
	WK_word packing_mask = LOW_BITS_MASK;

	/* loop to fetch words of input, splitting each into three
	 * words of output with 10 meaningful low bits.  This loop
	 * probably ought to be unrolled and maybe coiled
	 */
	while (input_next < input_end) {
		WK_word temp = input_next[0];

		output_next[0] = temp & packing_mask;
		output_next[1] = (temp >> 10) & packing_mask;
		output_next[2] = temp >> 20;

		input_next++;
		output_next += 3;
	}

	return output_next;
}

/*********************************************************************
 * WKdm_decompress --- THE DECOMPRESSOR
 * Expects WORD pointers to the source and destination buffers
 * and a page size in words.  The page size had better be 1024 unless
 * somebody finds the places that are dependent on the page size and
 * fixes them
 */

void
WKdm_decompress(WK_word* src_buf,
    WK_word* dest_buf,
    __unused unsigned int words)
{
	DictionaryElement dictionary[DICTIONARY_SIZE];

	/* arrays that hold output data in intermediate form during modeling */
	/* and whose contents are packed into the actual output after modeling */

	/* sizes of these arrays should be increased if you want to compress
	 * pages larger than 4KB
	 */
	WK_word tempTagsArray[300];  /* tags for everything          */
	WK_word tempQPosArray[300];  /* queue positions for matches  */
	WK_word tempLowBitsArray[1200]; /* low bits for partial matches */

	PRELOAD_DICTIONARY;

#ifdef WK_DEBUG
	printf("\nIn DECOMPRESSOR\n");
	printf("tempTagsArray is at %p\n", tempTagsArray);
	printf("tempQPosArray is at %p\n", tempQPosArray);
	printf("tempLowBitsArray is at %p\n", tempLowBitsArray);

	printf(" first four words of source buffer are:\n");
	printf("   %u\n   %u\n   %u\n   %u\n",
	    src_buf[0], src_buf[1], src_buf[2], src_buf[3]);

	{ int i;
	  WK_word *arr = (src_buf + TAGS_AREA_OFFSET + (PAGE_SIZE_IN_WORDS / 16));

	  printf("  first 20 full patterns are: \n");
	  for (i = 0; i < 20; i++) {
		  printf(" %d", arr[i]);
	  }
	  printf("\n");}
#endif

	WK_unpack_2bits(TAGS_AREA_START(src_buf),
	    TAGS_AREA_END(src_buf),
	    tempTagsArray);

#ifdef WK_DEBUG
	{ int i;
	  char* arr = (char *) tempTagsArray;

	  printf("  first 200 tags are: \n");
	  for (i = 0; i < 200; i++) {
		  printf(" %d", arr[i]);
	  }
	  printf("\n");}
#endif

	WK_unpack_4bits(QPOS_AREA_START(src_buf),
	    QPOS_AREA_END(src_buf),
	    tempQPosArray);

#ifdef WK_DEBUG
	{ int i;
	  char* arr = (char *) tempQPosArray;

	  printf("  first 200 queue positions are: \n");
	  for (i = 0; i < 200; i++) {
		  printf(" %d", arr[i]);
	  }
	  printf("\n");}
#endif

	WK_unpack_3_tenbits(LOW_BITS_AREA_START(src_buf),
	    LOW_BITS_AREA_END(src_buf),
	    tempLowBitsArray);

#ifdef WK_DEBUG
	printf("AFTER UNPACKING, about to enter main block \n");
#endif

	{
		char *next_tag = (char *) tempTagsArray;
		char *tags_area_end =
		    ((char *) tempTagsArray) + PAGE_SIZE_IN_WORDS;
		char *next_q_pos = (char *) tempQPosArray;
		WK_word *next_low_bits = tempLowBitsArray;
		WK_word *next_full_word = FULL_WORD_AREA_START(src_buf);

		WK_word *next_output = dest_buf;

#ifdef WK_DEBUG
		printf("next_output is %u\n", next_output);

		printf("next_tag is %u \n", next_tag);
		printf("tags_area_end is %u\n", tags_area_end);
		printf("next_q_pos is %u\n", next_q_pos);
		printf("next_low_bits is %u\n", next_low_bits);
		printf("next_full_word is %u\n", next_full_word);
#endif

		/* this loop should probably be unrolled. Maybe we should unpack
		 * as 4 bit values, giving two consecutive tags, and switch on
		 * that 16 ways to decompress 2 words at a whack
		 */
		while (next_tag < tags_area_end) {
			char tag = next_tag[0];

			switch (tag) {
			case ZERO_TAG: {
				*next_output = 0;
				break;
			}
			case EXACT_TAG: {
				WK_word *dict_location = dictionary + *(next_q_pos++);
				/* no need to replace dict. entry if matched exactly */
				*next_output = *dict_location;
				break;
			}
			case PARTIAL_TAG: {
				WK_word *dict_location = dictionary + *(next_q_pos++);
				{
					WK_word temp = *dict_location;

					/* strip out low bits */
					temp = ((temp >> NUM_LOW_BITS) << NUM_LOW_BITS);

					/* add in stored low bits from temp array */
					temp = temp | *(next_low_bits++);

					*dict_location = temp; /* replace old value in dict. */
					*next_output = temp; /* and echo it to output */
				}
				break;
			}
			case MISS_TAG: {
				WK_word missed_word = *(next_full_word++);
				WK_word *dict_location =
				    (WK_word *)
				    ((void *) (((char *) dictionary) + HASH_TO_DICT_BYTE_OFFSET(missed_word)));
				*dict_location = missed_word;
				*next_output = missed_word;
				break;
			}
			}
			next_tag++;
			next_output++;
		}

#ifdef WK_DEBUG
		printf("AFTER DECOMPRESSING\n");
		printf("next_output is %p\n", next_output);
		printf("next_tag is %p\n", next_tag);
		printf("next_full_word is %p\n", next_full_word);
		printf("next_q_pos is %p\n", next_q_pos);
#endif
	}
}