Changeset 230 in xtideuniversalbios for trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs

Timestamp:

Jan 29, 2012, 11:22:19 PM (13 years ago)

Author:

krille_n_@…

google:author:

krille_n_@hotmail.com

Message:

Changes to XTIDE Universal BIOS:

• Some small optimizations

File:

• trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm (modified) (5 diffs)

trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm

@@ -62 +62 @@
     jnz     SHORT .LimitAXtoMaxLCHScylinders
     cmp     ax, MAX_LCHS_CYLINDERS
-    jbe     SHORT .returnLCHS
+    jb      SHORT .returnLCHS
 .LimitAXtoMaxLCHScylinders:
     mov     ax, MAX_LCHS_CYLINDERS
@@ -71 +71 @@
     mov     ax, [di+DPT.wPchsCylinders]
     mov     bx, [di+DPT.wPchsHeadsAndSectors]
-    jmp     SHORT AccessDPT_ShiftPCHinAXBLtoLCH
+    ; Fall to AccessDPT_ShiftPCHinAXBLtoLCH
+
+
+;--------------------------------------------------------------------
+; AccessDPT_ShiftPCHinAXBLtoLCH
+;   Parameters:
+;       AX:     P-CHS cylinders (1...16383)
+;       BL:     P-CHS heads (1...16)
+;   Returns:
+;       AX:     Number of L-CHS cylinders (1...1024)
+;       BL:     Number of L-CHS heads (1...255)
+;       CX:     Number of bits shifted (4 at most)
+;   Corrupts registers:
+;       Nothing
+;--------------------------------------------------------------------
+AccessDPT_ShiftPCHinAXBLtoLCH:
+    xor     cx, cx
+.ShiftLoop:
+    cmp     ax, MAX_LCHS_CYLINDERS      ; Need to shift?
+    jbe     SHORT .LimitHeadsTo255      ;  If not, return
+    inc     cx                          ; Increment shift count
+    shr     ax, 1                       ; Halve cylinders
+    shl     bl, 1                       ; Double heads
+    jnz     SHORT .ShiftLoop
+.LimitHeadsTo255:                       ; DOS does not support drives with 256 heads
+    cmp     bl, cl                      ; Set CF if BL is zero
+    sbb     bl, ch                      ; If BL=0 then BL=255
+    ret
 
 
@@ -87 +114 @@
     mov     dx, [di+DPT.twLbaSectors+2]
     mov     bx, [di+DPT.twLbaSectors+4]
-    ret
-
-
-;--------------------------------------------------------------------
-; AccessDPT_ShiftPCHinAXBLtoLCH
-;   Parameters:
-;       AX:     P-CHS cylinders (1...16383)
-;       BL:     P-CHS heads (1...16)
-;   Returns:
-;       AX:     Number of L-CHS cylinders (1...1024)
-;       BL:     Number of L-CHS heads (1...255)
-;       CX:     Number of bits shifted
-;   Corrupts registers:
-;       Nothing
-;--------------------------------------------------------------------
-AccessDPT_ShiftPCHinAXBLtoLCH:
-    xor     cx, cx
-.ShiftLoop:
-    cmp     ax, MAX_LCHS_CYLINDERS      ; Need to shift?
-    jbe     SHORT .LimitHeadsTo255      ;  If not, return
-    inc     cx                          ; Increment shift count
-    shr     ax, 1                       ; Halve cylinders
-    shl     bl, 1                       ; Double heads
-    jmp     SHORT .ShiftLoop
-.LimitHeadsTo255:                       ; DOS does not support drives with 256 heads
-    cmp     bl, cl                      ; Set CF if BL is zero
-    sbb     bl, ch                      ; If BL=0 then BL=255
     ret
 
@@ -143 +143 @@
 ;       DS:DI:  Ptr to Disk Parameter Table
 ;   Returns:
-;       AL:     Addressing Mode (L-CHS, P-CHS, LBA28, LBA48) 
+;       AL:     Addressing Mode (L-CHS, P-CHS, LBA28, LBA48)
 ;               unshifted (still shifted where it is in bFlagsLow)
 ;       ZF:     Set based on value in AL
@@ -149 +149 @@
 ;       AL
 ;--------------------------------------------------------------------
-; 
-; Converted to a macro since only called in two places, and the call/ret overhead 
+;
+; Converted to a macro since only called in two places, and the call/ret overhead
 ; is not worth it for these two instructions (4 bytes total)
 ;