Added a quick comparison between ramcrc32bd and ramrsbd

A bit more manual than I would've liked, compiled with:

  CC='arm-none-eabi-gcc -static -mthumb' CFLAGS='-DLFS_NO_DEBUG -DLFS_NO_WARN -DLFS_NO_ERROR -DLFS_NO_ASSERT' make code stack

But then manually removed unused functions that couldn't be gced with
available info:

- ramrsbd_gf_p_scale (unused, ramrsbd_gf_p_xors overlaps)
- ramrsbd_gf_p_xor   (unused, ramrsbd_gf_p_xors overlaps)
- lfs_crc            (unused in ramrsbd)
- rtable.0/RAMRSBD_GF_LOG/RAMRSBD_GF_POW (attributes to tables)
- ramrsbd_gf_divmod  (unused, ramrsbd_gf_p_divmod1 overlaps)

Note the code/stack cost does NOT include the related table/buffer
costs.

Makefile

@@ -20,7 +20,7 @@ PERF	 ?= perf
 
 SRC  ?= $(filter-out \
 		$(wildcard *.t.* *.b.* littlefs/*.t.* littlefs/*.b.*), \
-		$(wildcard *.c littlefs/*.c))
+		$(wildcard *.c littlefs/lfs_util.c))
 OBJ  := $(SRC:%.c=$(BUILDDIR)/%.o)
 DEP  := $(SRC:%.c=$(BUILDDIR)/%.d)
 ASM  := $(SRC:%.c=$(BUILDDIR)/%.s)

README.md

@@ -55,6 +55,13 @@ available. But the same idea can be extended to any other CRC, as long
 as it has a sufficient [Hamming distance][hamming-distance] for the
 expected number of bit-errors.
 
+A quick comparison of current ram-ecc-bds:
+
+|            | code   | tables | stack | buffers  | runtime                  |
+|:-----------|-------:|-------:|------:|---------:|-------------------------:|
+| ramcrc32bd |  940 B |   64 B |  88 B |      0 B |      $O\left(n^e\right)$ |
+| ramrsbd    | 1430 B |  512 B | 128 B | n + 4e B | $O\left(ne + e^2\right)$ |
+
 See also:
 
 - [littlefs][littlefs]

ramcrc32bd.c

@@ -320,6 +320,7 @@ int ramcrc32bd_erase(const struct lfs_config *cfg, lfs_block_t block) {
     LFS_ASSERT(block < cfg->block_count);
 
     // erase is a noop
+    (void)cfg;
     (void)block;
 
     RAMCRC32BD_TRACE("ramcrc32bd_erase -> %d", 0);