Hello
The _divulong function use a bool variables, but this is not optimal:
- this force the use of the "T" reg as soon as a 32bit division is used on
mcs51, thus potentially reducing the stack size up to 24 bytes.
- This force the compiler to use a bit, which produce suboptimal code
- This does not reduce stack useage as the compiler can allocate the bool
variable to a register
The following patch use a unsigned char for the boolean variable the generated
code is changed as following for the large stack auto code model:
;x Allocated to stack - _bp +1
;reste Allocated to registers r2 r3 r6 r7
;count Allocated to registers r5
-;c Allocated to registers b0
+;c Allocated to registers r4
;------------------------------------------------------------
; _divulong.c:335: _divulong (unsigned long x, unsigned long y)
; -----------------------------------------
@@ -148,8 +134,6 @@
rl a
anl a,#0x01
mov r4,a
- add a,#0xff
- mov b0,c
; _divulong.c:345: x <<= 1;
mov r0,_bp
inc r0
@@ -182,7 +166,8 @@
rlc a
mov r7,a
; _divulong.c:347: if (c)
- jnb b0,00102$
+ mov a,r4
+ jz 00102$
; _divulong.c:348: reste |= 1L;
orl ar2,#0x01
00102$:
On cc253x SoC this lead to a reduction of 4 byte in code size and 5 cycle per
loop iteration, thus saving 160 cycle on a 32bits division.
Thanks,
Philippe
Index: device/lib/_divulong.c
===================================================================
--- device/lib/_divulong.c (révision 7100)
+++ device/lib/_divulong.c (copie de travail)
@@ -336,7 +336,7 @@
{
unsigned long reste = 0L;
unsigned char count = 32;
- BOOL c;
+ unsigned char c;
do
{
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