Reverted 16-bit mbid/mrid mids to full 32-bits

The possibility of 16-bit mbid/mrids being a problematic limit is too
high for me to be able to confidently move forward with this internal
encoding.

Consider a filesystem with small blocks and/or large amounts of metadata
per file. If a single file almost fills up an mdir, it risks an
effective limit on the filesystem of 2^16 files. Not a deal-breaker, but
certainly a surprising limit on a supposed "32-bit" filesystem.

We can add more granular integer-limit configurations, but with simple
configurations, the option to increase the integer-limit filesystem-wide
to 64-bits would cost more RAM than just increasing the mbid/mrids
limits.

Though this is always up for reconsideration in the future.

            code          stack
  before:  20762           1720
  after:   20590 (-0.8%)   1784 (+3.7%)

It's interesting to not the code/RAM tradeoff here. RAM sees a
significant hit, but code improves, likely because of better instruction
sequences for 32-bit operations (this is targeting ARM thumb,
32-bit MCUs).

Though the code savings likely varies widely across instruction sets,
and I would guess swings negative on 16/8-bit MCUs.

lfs.c

@@ -1539,9 +1539,11 @@ static int lfsr_data_readecksum(lfs_t *lfs, lfsr_data_t *data,
 #define LFSR_MID(_bid, _rid) ((lfsr_mid_t){.bid=_bid, .rid=_rid})
 
 static inline int lfsr_mid_cmp(lfsr_mid_t a, lfsr_mid_t b) {
-    int32_t a_w = ((int32_t)a.bid << 16) | (int32_t)a.rid;
-    int32_t b_w = ((int32_t)b.bid << 16) | (int32_t)b.rid;
-    return a_w - b_w;
+    if (a.bid != b.bid) {
+        return a.bid - b.bid;
+    }
+
+    return a.rid - b.rid;
 }
 
 // we use the root's bookmark at 0.0 to represent root
@@ -1637,13 +1639,13 @@ static int lfsr_grm_todisk(lfs_t *lfs, const lfsr_grm_t *grm,
     for (uint8_t i = 0; i < count; i++) {
         // map mid=-1 (mroot) to mid=0
         lfs_ssize_t d_ = lfs_toleb128(
-                lfs_smax32(grm->mids[i].bid, 0), &buffer[d], 3);
+                lfs_smax32(grm->mids[i].bid, 0), &buffer[d], 5);
         if (d_ < 0) {
             return d_;
         }
         d += d_;
 
-        d_ = lfs_toleb128(grm->mids[i].rid, &buffer[d], 3);
+        d_ = lfs_toleb128(grm->mids[i].rid, &buffer[d], 5);
         if (d_ < 0) {
             return d_;
         }
@@ -1677,14 +1679,12 @@ static int lfsr_data_readgrm(lfs_t *lfs, lfsr_data_t *data,
         if (err) {
             return err;
         }
-        LFS_ASSERT(bid <= 0x7fff);
 
         lfs_ssize_t rid;
         err = lfsr_data_readleb128(lfs, data, &rid);
         if (err) {
             return err;
         }
-        LFS_ASSERT(rid < 0x7fff);
 
         // adjust mid if mtree is inlined
         LFS_ASSERT(lfsr_mtree_isinlined(lfs)
@@ -6180,13 +6180,13 @@ static int lfsr_mtree_traversal_next(lfs_t *lfs,
 // - 32-bit block_size   => 5 byte leb128 (worst case)
 // - 32-bit block_count  => 5 byte leb128 (worst case)
 // - 7-bit utag_limit    => 1 byte leb128 (worst case)
-// - 16-bit mtree_limit  => 3 byte leb128 (worst case)
+// - 32-bit mtree_limit  => 5 byte leb128 (worst case)
 // - 32-bit attr_limit   => 5 byte leb128 (worst case)
 // - 32-bit name_limit   => 5 byte leb128 (worst case)
 // - 32-bit file_limit   => 5 byte leb128 (worst case)
 //                       => 33 bytes total
 // 
-#define LFSR_SUPERCONFIG_DSIZE (1+1+1+1+5+5+1+3+5+5+5)
+#define LFSR_SUPERCONFIG_DSIZE (1+1+1+1+5+5+1+5+5+5+5)
 
 static lfs_ssize_t lfsr_superconfig_todisk(lfs_t *lfs,
         uint8_t buffer[static LFSR_SUPERCONFIG_DSIZE]) {
@@ -6224,7 +6224,7 @@ static lfs_ssize_t lfsr_superconfig_todisk(lfs_t *lfs,
     d += 1;
 
     // on-disk mtree limit
-    d_ = lfs_toleb128(0x7fff, &buffer[d], 3);
+    d_ = lfs_toleb128(0x7fffffff, &buffer[d], 5);
     if (d_ < 0) {
         return d_;
     }
@@ -6447,11 +6447,11 @@ static int lfsr_mountinited(lfs_t *lfs) {
                     return err;
                 }
 
-                if (err || mtree_limit != 0x7fff) {
+                if (err || mtree_limit != 0x7fffffff) {
                     LFS_ERROR("Incompatible mdir limit 0x%"PRIx32
                             " (> 0x%"PRIx32")",
                             (err ? -1 : mtree_limit),
-                            0x7fff);
+                            0x7fffffff);
                     return LFS_ERR_INVAL;
                 }
 

lfs.h

@@ -47,10 +47,10 @@ typedef uint32_t lfs_block_t;
 typedef uint16_t lfsr_tag_t;
 typedef int16_t lfsr_stag_t;
 
-typedef uint16_t lfsr_mbid_t;
-typedef int16_t lfsr_smbid_t;
-typedef uint16_t lfsr_mrid_t;
-typedef int16_t lfsr_smrid_t;
+typedef uint32_t lfsr_mbid_t;
+typedef int32_t lfsr_smbid_t;
+typedef uint32_t lfsr_mrid_t;
+typedef int32_t lfsr_smrid_t;
 
 typedef struct lfsr_mid {
     lfsr_smbid_t bid;
@@ -405,11 +405,11 @@ typedef struct lfsr_openedmdir {
 
 // space for:
 // - type - 1 leb128 - 1 byte (worst case)
-// - mid0 - 1 leb128 - 3 bytes (worst case)
-// - rid0 - 1 leb128 - 3 bytes (worst case)
-// - mid1 - 1 leb128 - 3 bytes (worst case)
-// - rid1 - 1 leb128 - 3 bytes (worst case)
-#define LFSR_GRM_DSIZE (1+3+3+3+3)
+// - mid0 - 1 leb128 - 5 bytes (worst case)
+// - rid0 - 1 leb128 - 5 bytes (worst case)
+// - mid1 - 1 leb128 - 5 bytes (worst case)
+// - rid1 - 1 leb128 - 5 bytes (worst case)
+#define LFSR_GRM_DSIZE (1+5+5+5+5)
 
 typedef struct lfsr_grm {
     lfsr_mid_t mids[2];