chain/utility.c: Adjust lba2chs

This tiny patch adjusts how lba2chs() deals with unknown geometries.
Instead of returning max values of "typical" geometries, it returns
chs values calculated from them.

Signed-off-by: Michal Soltys <soltys@ziu.info>

diff --git a/com32/chain/utility.c b/com32/chain/utility.c
index 828c85e..9824952 100644 (file)
--- a/com32/chain/utility.c
+++ b/com32/chain/utility.c
@@ -51,37 +51,40 @@ void wait_key(void)
 uint32_t lba2chs(const struct disk_info *di, uint64_t lba)
 {
     uint32_t c, h, s, t;
+    uint32_t cs, hs, ss;
 
+    /*
+     * Not much reason here, but if we have no valid chs geometry, we assume
+     * "typical" ones to have something to return.
+     */
     if (di->cbios) {
-       if (lba >= di->cyl * di->head * di->sect) {
-           s = di->sect;
-           h = di->head - 1;
-           c = di->cyl - 1;
-           goto out;
+       cs = di->cyl;
+       hs = di->head;
+       ss = di->sect;
+    } else {
+       if (di->disk & 0x80) {
+           cs = 1024;
+           hs = 255;
+           ss = 63;
+       } else {
+           cs = 80;
+           hs = 2;
+           ss = 18;
        }
-       s = ((uint32_t)lba % di->sect) + 1;
-       t = (uint32_t)lba / di->sect;
-       h = t % di->head;
-       c = t / di->head;
-    } else
-       goto fallback;
+    }
 
-out:
-    return h | (s << 8) | ((c & 0x300) << 6) | ((c & 0xFF) << 16);
+    if (lba >= cs*hs*ss) {
+       s = ss;
+       h = hs - 1;
+       c = cs - 1;
+    } else {
+       s = ((uint32_t)lba % ss) + 1;
+       t = (uint32_t)lba / ss;
+       h = t % hs;
+       c = t / hs;
+    }
 
-fallback:
-    if (di->disk & 0x80)
-       return 0x00FFFFFE; /* 1023/63/254 */
-    else
-       /*
-        * adjust ?
-        * this is somewhat "useful" with partitioned floppy,
-        * maybe stick to 2.88mb ?
-        */
-       return 0x004F1201; /* 79/18/1 */
-#if 0
-       return 0x004F2401; /* 79/36/1 */
-#endif
+    return h | (s << 8) | ((c & 0x300) << 6) | ((c & 0xFF) << 16);
 }
 
 uint32_t get_file_lba(const char *filename)