Changeset 75248 in vbox

Timestamp:

Nov 5, 2018 10:35:20 AM (6 years ago)

Author:

vboxsync

Message:

BIOS: Fast path for 32-bit division when divisor is in fact only 16-bit.

File:

• trunk/src/VBox/Devices/BiosCommonCode/__U4D.asm (modified) (1 diff)

trunk/src/VBox/Devices/BiosCommonCode/__U4D.asm

@@ -72 +72 @@
                 .8086
 else
+                ;
+                ; If the divisor is only 16-bit, use a fast path
+                ;
+                test    cx, cx
+                jnz     do_it_the_hard_way
+                
+                div     bx              ; dx:ax / bx -> ax=quotient, dx=remainder
 
+                mov     bx, dx          ; remainder in cx:bx, and we know cx=0
+
+                xor     dx, dx          ; quotient in dx:ax, dx must be zero
+
+                popf
+                ret
+
+do_it_the_hard_way:
                 ; Call C function do this.
                 push    ds