diff options
| author | Keith Packard <keithp@keithp.com> | 2013-03-28 17:38:14 -0700 |
|---|---|---|
| committer | Keith Packard <keithp@keithp.com> | 2013-03-28 17:38:14 -0700 |
| commit | 44e418bbecd3a3deae942803141cf115d92f29d2 (patch) | |
| tree | 27a7663db6e0e29d5b28d836e0a18ad6b13d6c64 /src | |
| parent | 8101e4af199a3d79bff434f788cce9f97aeac53a (diff) | |
altos: seek forward on FAT cluster chain instead of restarting
This improves sequential file performance by taking advantage of any
previous cached cluster/offset pair and starting from there when the
cluster changes rather than starting from scratch at the begining again.
Signed-off-by: Keith Packard <keithp@keithp.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/drivers/ao_fat.c | 24 |
1 files changed, 12 insertions, 12 deletions
diff --git a/src/drivers/ao_fat.c b/src/drivers/ao_fat.c index 65c5ea7c..98f57d67 100644 --- a/src/drivers/ao_fat.c +++ b/src/drivers/ao_fat.c @@ -375,10 +375,20 @@ ao_fat_current_sector(void) sector_offset = ao_file_offset >> SECTOR_SHIFT; - if (!ao_file_cluster) { + if (!ao_file_cluster || ao_file_offset < ao_file_cluster_offset) { + ao_file_cluster = ao_file_dirent.cluster; + ao_file_cluster_offset = 0; + } + + if (ao_file_cluster_offset + bytes_per_cluster <= ao_file_offset) { + uint16_t cluster_distance; + cluster_offset = sector_offset / sectors_per_cluster; - cluster = ao_fat_cluster_seek(ao_file_dirent.cluster, cluster_offset); + cluster_distance = cluster_offset - ao_file_cluster_offset / bytes_per_cluster; + + cluster = ao_fat_cluster_seek(ao_file_cluster, cluster_distance); + if (!ao_fat_cluster_valid(cluster)) return 0xffffffff; ao_file_cluster = cluster; @@ -392,16 +402,6 @@ ao_fat_current_sector(void) static void ao_fat_set_offset(uint32_t offset) { - - if (offset == 0) { - ao_file_cluster = ao_file_dirent.cluster; - ao_file_cluster_offset = 0; - } - else if (offset < ao_file_cluster_offset || - ao_file_cluster_offset + bytes_per_cluster <= offset) - { - ao_file_cluster = 0; - } ao_file_offset = offset; } |