X-Git-Url: https://wimlib.net/git/?a=blobdiff_plain;f=include%2Fwimlib%2Flz_sarray.h;h=e609d0c2e79dbbcc93a668475ae0f4fa6a53d0dd;hb=2fdc3bd720f5bc49680dc2284ea42a537d1acc07;hp=6f878dd2bafd9d89b9d16ba80b88d70fa46e5217;hpb=31274ba5cbf4de73c8a68e7d17f490c3b0df6cff;p=wimlib

diff --git a/include/wimlib/lz_sarray.h b/include/wimlib/lz_sarray.h
index 6f878dd2..e609d0c2 100644
--- a/include/wimlib/lz_sarray.h
+++ b/include/wimlib/lz_sarray.h
@@ -34,7 +34,8 @@
 #ifndef _WIMLIB_LZ_SARRAY_H
 #define _WIMLIB_LZ_SARRAY_H
 
-#include "wimlib/compiler.h" /* must define '_always_inline_attribute'  */
+#include "wimlib/compiler.h" /* must define '_always_inline_attribute',
+				'likely()', and 'prefetch()'.  */
 #include "wimlib/lz.h"       /* must define 'struct raw_match' and LZ_ASSERT()  */
 #include "wimlib/types.h"    /* must define 'bool', 'u8', 'u16, and 'u32'  */
 
@@ -135,9 +136,9 @@ struct salink {
 		struct {
 			/* Intially, the length, in bytes, of the longest common
 			 * prefix (LCP) between the suffix having this rank and
-			 * the suffix with the the smallest larger rank that
+			 * the suffix with the smallest larger rank that
 			 * starts earlier in the window than the suffix having
-			 * this rank.
+			 * this rank.  If no such suffix exists, this will be 0.
 			 *
 			 * Later, during match-finding, after the corresponding
 			 * suffix has entered the LZ77 dictionary, this value
@@ -149,9 +150,10 @@ struct salink {
 
 			/* Initially, the length, in bytes, of the longest
 			 * common prefix (LCP) between the suffix having this
-			 * rank and the suffix with the the largest smaller rank
+			 * rank and the suffix with the largest smaller rank
 			 * that starts earlier in the window than the suffix
-			 * having this rank.
+			 * having this rank.  If no such suffix exists, this
+			 * will be 0.
 			 *
 			 * Later, during match-finding, after the corresponding
 			 * suffix has entered the LZ77 dictionary, this value
@@ -163,22 +165,24 @@ struct salink {
 
 			/* Distance to the suffix referred to in the description
 			 * of "lcpnext" above, but capped to a maximum value to
-			 * save memory.  If the true distance was truncated,
-			 * this will give the distance to the rank of a suffix
-			 * that is lexicographically closer to the current
-			 * suffix than the desired suffix, but appears *later*
-			 * in the window and hence cannot be used as the basis
-			 * for a LZ77 match.  */
+			 * save memory; or, 0 if no such suffix exists.  If the
+			 * true distance was truncated, this will give the
+			 * distance to the rank of a suffix that is
+			 * lexicographically closer to the current suffix than
+			 * the desired suffix, but appears *later* in the window
+			 * and hence cannot be used as the basis for an LZ77
+			 * match.  */
 			lz_sarray_delta_t dist_to_next;
 
 			/* Distance to the suffix referred to in the description
 			 * of "lcpprev" above, but capped to a maximum value to
-			 * save memory.  If the true distance was truncated,
-			 * this will give the distance to the rank of a suffix
-			 * that is lexicographically closer to the current
-			 * suffix than the desired suffix, but appears *later*
-			 * in the window and hence cannot be used as the basis
-			 * for a LZ77 match.  */
+			 * save memory; or, 0 if no such suffix exists.  If the
+			 * true distance was truncated, this will give the
+			 * distance to the rank of a suffix that is
+			 * lexicographically closer to the current suffix than
+			 * the desired suffix, but appears *later* in the window
+			 * and hence cannot be used as the basis for an LZ77
+			 * match.  */
 			lz_sarray_delta_t dist_to_prev;
 		};
 	};
@@ -282,6 +286,19 @@ lz_sarray_get_matches(struct lz_sarray *mf,
 	/* Prepare for searching the current position.  */
 	lz_sarray_update_salink(r, link);
 
+#if 1
+	/* Prefetch next position in SA and link.
+	 *
+	 * This can improve performance on large windows since the locations in
+	 * SA and link at which each successive search begins are in general
+	 * randomly distributed.  */
+	if (likely(i + 1 < mf->window_size)) {
+		const lz_sarray_pos_t next_r = ISA[i + 1];
+		prefetch(&SA[next_r]);
+		prefetch(&link[next_r]);
+	}
+#endif
+
 	/* L = rank of next suffix to the left;
 	 * R = rank of next suffix to the right;
 	 * lenL = length of match between current position and the suffix with rank L;
@@ -315,7 +332,7 @@ lz_sarray_get_matches(struct lz_sarray *mf,
 	u32 count_remaining = max_matches_to_consider;
 
 	/* pending_offset = offset of lowest-cost match found for the current
-	 * length, or 0 if no match has been found yet.  */
+	 * length, or 0 if none found yet.  */
 	lz_sarray_pos_t pending_offset = 0;
 
 	/* Note: some 'goto' statements are used in the remainder of this
@@ -367,7 +384,7 @@ extend_left:
 			}
 		}
 
-		/* Advance left to next suffix.  */
+		/* Advance left to previous suffix.  */
 
 		old_L = L;
 		old_lenL = lenL;
@@ -406,10 +423,10 @@ extend_left:
 				}
 			}
 
-			/* Here we have lenL < lenR.  Extend right, unless the
-			 * minimum match length would be underrun.  */
-			if (lenR == 0)
-				return nmatches;
+			/* Here we have lenL < lenR.  Extend right.
+			 * (No check for whether the minimum match length has
+			 * been underrun is needed, provided that such lengths
+			 * are marked as 0.)  */
 			goto extend_right;
 		}
 	}
@@ -479,13 +496,7 @@ extend_right:
 				pending_offset = 0;
 			}
 
-			if (lenR > lenL) {
-				/* lenR > lenL:  Keep extending right, unless
-				 * the minimum match length would be underrun.
-				 */
-				if (lenR == 0)
-					return nmatches;
-			} else {
+			if (lenL >= lenR) {
 				/* lenL >= lenR:  Extend left, unless the
 				 * minimum match length would be underrun, in
 				 * which case we are done.  */
@@ -494,6 +505,10 @@ extend_right:
 
 				goto extend_left;
 			}
+			/* lenR > lenL:  Keep extending right.
+			 * (No check for whether the minimum match length has
+			 * been underrun is needed, provided that such lengths
+			 * are marked as 0.)  */
 		}
 	}
 }