Some small tweaks

- Moved alt encoding 0x1 => 0x4, which can lead to slightly better
  lookup tables, the perturb bit takes the same place as the color bit,
  which means both can be ignored in readonly operations.

- Dropped lfs_rbyd_fetchmatch, asking each lfs_rbyd_fetch to include NULL
  isn't that bad.

New encoding:

  tags:
  iiii iiiiiii iiiiiTT TTTTTTt ttt0tpv
                   ^--------^------^^^- 16-bit id
                            '------|||- 8-bit type2
                                   '||- 5-bit type1
                                    '|- perturb bit
                                     '- valid bit
  llll lllllll lllllll lllllll lllllll
                                     ^- n-bit length

  alts:
  wwww wwwwwww wwwwwww wwwwwww www1dcv
                                 ^^^-^- 28-bit weight
                                  '|-|- color bit
                                   '-|- direction bit
                                     '- valid bit
  jjjj jjjjjjj jjjjjjj jjjjjjj jjjjjjj
                                     ^- n-bit jump

lfs.c

@@ -407,10 +407,13 @@ enum lfs_rtag_type1 {
     LFS_TYPE1_GSTATE = 0x10,
 
     LFS_TYPE1_CRC0   = 0x02,
-    LFS_TYPE1_CRC1   = 0x0a,
+    LFS_TYPE1_CRC1   = 0x03,
-    LFS_TYPE1_FCRC   = 0x12,
+    LFS_TYPE1_FCRC   = 0x0a,
 
-    LFS_TYPE1_ALT    = 0x01,
+    LFS_TYPE1_ALTBLT = 0x04,
+    LFS_TYPE1_ALTRLT = 0x05,
+    LFS_TYPE1_ALTBGT = 0x06,
+    LFS_TYPE1_ALTRGT = 0x07,
 };
 
 enum lfs_rtag_color {
@@ -432,8 +435,8 @@ enum lfs_rtag_dir {
     LFS_MKRTAG_(LFS_TYPE1_##type1, type2, id)
 
 #define LFS_MKRALT_(color, dir, weight) \
-    (0x1 \
+    (LFS_TYPE1_ALTBLT \
-        | ((0x1 & (lfs_rtag_t)(color)) << 2) \
+        | ((0x1 & (lfs_rtag_t)(color)) << 0) \
         | ((0x1 & (lfs_rtag_t)(dir)) << 1) \
         | ((0xfffffff & (lfs_rtag_t)(weight)) << 3))
 
@@ -445,11 +448,11 @@ static inline bool lfs_rtag_isvalid(lfs_rtag_t tag) {
 }
 
 static inline bool lfs_rtag_isalt(lfs_rtag_t tag) {
-    return tag & 0x1;
+    return tag & 0x4;
 }
 
 static inline bool lfs_rtag_intree(lfs_rtag_t tag) {
-    return tag & 0x2;
+    return !(tag & 0x6);
 }
 
 static inline uint8_t lfs_rtag_type1(lfs_rtag_t tag) {
@@ -473,11 +476,11 @@ static inline bool lfs_rtag_isgt(lfs_rtag_t tag) {
 }
 
 static inline bool lfs_rtag_isblack(lfs_rtag_t tag) {
-    return !(tag & 0x4);
+    return !(tag & 0x1);
 }
 
 static inline bool lfs_rtag_isred(lfs_rtag_t tag) {
-    return tag & 0x4;
+    return tag & 0x1;
 }
 
 static inline lfs_rtag_t lfs_rtag_weight(lfs_rtag_t tag) {
@@ -485,11 +488,11 @@ static inline lfs_rtag_t lfs_rtag_weight(lfs_rtag_t tag) {
 }
 
 static inline lfs_rtag_t lfs_rtag_red(lfs_rtag_t tag) {
-    return tag | 0x4;
+    return tag | 0x1;
 }
 
 static inline lfs_rtag_t lfs_rtag_black(lfs_rtag_t tag) {
-    return tag & ~0x4;
+    return tag & ~0x1;
 }
 
 static inline lfs_rtag_t lfs_rtag_parallel(lfs_rtag_t a, lfs_rtag_t b) {
@@ -895,7 +898,7 @@ static lfs_ssize_t lfs_rbyd_readtag(lfs_t *lfs,
     return i;
 }
 
-static int lfs_rbyd_fetchmatch(lfs_t *lfs,
+static int lfs_rbyd_fetch(lfs_t *lfs,
         lfs_rbyd_t *rbyd, lfs_block_t block,
         struct lfs_fetchpattern *patterns) {
     // read the revision count and get the crc started
@@ -941,7 +944,7 @@ static int lfs_rbyd_fetchmatch(lfs_t *lfs,
         }
 
         // found trunk of tree?
-        if (!wastrunk && (lfs_rtag_isalt(tag) || lfs_rtag_intree(tag))) {
+        if (!wastrunk && lfs_rtag_intree(tag)) {
             trunk = off;
             wastrunk = true;
         }
@@ -962,7 +965,7 @@ static int lfs_rbyd_fetchmatch(lfs_t *lfs,
         }
 
         // not an end-of-commit crc
-        if ((lfs_rtag_type1(tag) & ~0x8) != LFS_TYPE1_CRC0) {
+        if ((lfs_rtag_type1(tag) & ~0x1) != LFS_TYPE1_CRC0) {
             // fcrc is only valid if the last tag was a crc
             hasfcrc = false;
 
@@ -1056,10 +1059,6 @@ static int lfs_rbyd_fetchmatch(lfs_t *lfs,
     return 0;
 }
 
-static int lfs_rbyd_fetch(lfs_t *lfs, lfs_rbyd_t *rbyd, lfs_block_t block) {
-    return lfs_rbyd_fetchmatch(lfs, rbyd, block, NULL);
-}
-
 //static lfs_ssize_t lfs_rbyd_lookup(lfs_t *lfs, lfs_rbyd_t *rbyd,
 //        lfs_rtag_t tag, lfs_off_t *off, lfs_rtag_t *ntag) {
 //    // TODO
@@ -1474,8 +1473,8 @@ static int lfs_rbyd_commit(lfs_t *lfs, lfs_rbyd_t *rbyd,
     // so we can really change any bit to make this happen, we've reserved a bit
     // in crc tags just for this purpose
     if ((lfs_popc(crc) & 1) == (perturb & 1)) {
-        buffer[0] ^= 0x10;
+        buffer[0] ^= 0x2;
-        crc ^= 0xc00c303e; // note crc(a ^ b) == crc(a) ^ crc(b)
+        crc ^= 0xdb8ca0c3; // note crc(a ^ b) == crc(a) ^ crc(b)
     }
     lfs_tole32_(crc, &buffer[1+5]);
 

scripts/dbgrbyd.py

@@ -45,15 +45,7 @@ def tagrepr(tag, size, off=None):
     type2 = (tag >> 7) & 0xff
     id = (tag >> 15) & 0xffff
 
-    if type1 & 1:
+    if type1 == 0x40:
-        return 'alt %s %s x%x %s' % (
-            'r' if type1 & 4 else 'b',
-            'gt' if type1 & 2 else 'lt',
-            tag >> 3,
-            'x%x' % (0xffffffff & (off-size))
-                if off is not None
-                else '-%d' % off)
-    elif type1 == 0x40:
         return 'create x%02x id%d %d' % (type2, id, size)
     elif type1 == 0x48:
         return 'delete x%02x id%d %d' % (type2, id, size)
@@ -68,16 +60,24 @@ def tagrepr(tag, size, off=None):
             return 'tail x%02x %d' % (type2, size)
     elif type1 == 0x10:
         return 'gstate x%02x %d' % (type2, size)
-    elif type1 == 0x02 or type1 == 0x0a:
+    elif (type1 & 0x7e) == 0x02:
         if type2 == 0:
             return 'crc%x %d' % (type1 >> 3, size)
         else:
             return 'crc%x x%02x %d' % (type1 >> 3, type2, size)
-    elif type1 == 0x12:
+    elif type1 == 0x0a:
         if type2 == 0:
             return 'fcrc %d' % (size)
         else:
             return 'fcrc x%02x %d' % (type2, size)
+    elif type1 & 0x4:
+        return 'alt%s%s x%x %s' % (
+            'r' if type1 & 4 else 'b',
+            'gt' if type1 & 2 else 'lt',
+            tag >> 3,
+            'x%x' % (0xffffffff & (off-size))
+                if off is not None
+                else '-%d' % off)
     else:
         return 'x%02x x%02x id%d %d' % (type1, type2, id, size)
 
@@ -104,8 +104,8 @@ def main(disk, block_size, block1, block2=None, **args):
             crc = crc32c(data[j:j+delta], crc)
             j += delta
 
-            if not tag & 0x1:
+            if not tag & 0x4:
-                if (tag & 0x37) != 0x2:
+                if (tag & 0x7e) != 0x2:
                     crc = crc32c(data[j:j+size], crc)
                 # found a crc?
                 else:
@@ -131,11 +131,10 @@ def main(disk, block_size, block1, block2=None, **args):
 
     # print contents of the winning metadata block
     block, data, rev, off = blocks[i], datas[i], revs[i], offs[i]
-    print('mdir 0x%x, rev %d, size %d (was 0x%x, %d, %d)' % (
+    print('mdir 0x%x, rev %d, size %d%s' % (
         block, rev, off,
-        blocks[len(blocks)-1-i],
+        ' (was 0x%x, %d, %d)' % (blocks[~i], revs[~i], offs[~i])
-        revs[len(revs)-1-i],
+            if len(blocks) > 1 else ''))
-        offs[len(offs)-1-i]))
     print('%-8s  %-22s  %s' % (
         'off', 'tag',
         'data (truncated)'
@@ -158,8 +157,8 @@ def main(disk, block_size, block1, block2=None, **args):
         crc = crc32c(data[j:j+delta], crc)
         j += delta
 
-        if not tag & 0x1:
+        if not tag & 0x4:
-            if (tag & 0x37) != 0x2:
+            if (tag & 0x7e) != 0x2:
                 crc = crc32c(data[j:j+size], crc)
             # found a crc?
             else:
@@ -173,7 +172,7 @@ def main(disk, block_size, block1, block2=None, **args):
             '%-22s%s' % (
                 tagrepr(tag, size, j_),
                 '  %s' % next(xxd(data[j_+delta:j_+delta+min(size, 8)], 8), '')
-                    if not tag & 1 and not args.get('no_truncate') else ''),
+                    if not tag & 0x4 and not args.get('no_truncate') else ''),
             '  (%s)' % ', '.join(notes)
                 if notes else ''))
 
@@ -181,7 +180,7 @@ def main(disk, block_size, block1, block2=None, **args):
             for o, line in enumerate(xxd(data[j_:j_+delta])):
                 print('%8s: %s' % ('%04x' % (j_ + o*16), line))
 
-        if not tag & 0x1:
+        if not tag & 0x4:
             if args.get('raw') or args.get('no_truncate'):
                 for o, line in enumerate(xxd(data[j_+delta:j_+delta+size])):
                     print('%8s: %s' % ('%04x' % (j_+delta + o*16), line))

tests/test_rbyd.toml

@@ -22,14 +22,14 @@ code = '''
     lfs_rbyd_t rbyd_ = rbyd;
     lfs_bd_erase(&lfs, rbyd_.block) => 0;
     lfs_rbyd_commit(&lfs, &rbyd_, NULL) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
     // commit with one attribute
     rbyd_ = rbyd;
     lfs_bd_erase(&lfs, rbyd_.block) => 0;
     lfs_rbyd_commit(&lfs, &rbyd_,
             LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
     // commit with two attributes
     rbyd_ = rbyd;
@@ -38,7 +38,7 @@ code = '''
             LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4,
             LFS_MKRATTR(UATTR, 2, 0, &(uint32_t){0xbbbbbbbb}, 4,
             NULL))) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
 //    // commit with three attributes
 //    rbyd_ = rbyd;
@@ -74,7 +74,7 @@ code = '''
     lfs_rbyd_t rbyd_ = rbyd;
     lfs_bd_erase(&lfs, rbyd_.block) => 0;
     lfs_rbyd_commit(&lfs, &rbyd_, NULL) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
     // commit with one attribute
     rbyd_ = rbyd;
@@ -82,7 +82,7 @@ code = '''
     lfs_rbyd_commit(&lfs, &rbyd_, NULL) => 0;
     lfs_rbyd_commit(&lfs, &rbyd_,
             LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
     // commit with two attributes
     rbyd_ = rbyd;
@@ -91,7 +91,7 @@ code = '''
             LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
     lfs_rbyd_commit(&lfs, &rbyd_,
             LFS_MKRATTR(UATTR, 2, 0, &(uint32_t){0xbbbbbbbb}, 4, NULL)) => 0;
-    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block) => 0;
+    lfs_rbyd_fetch(&lfs, &rbyd_, rbyd.block, NULL) => 0;
 
 //    // commit with three attributes
 //    rbyd_ = rbyd;