# [Issue 5607] New: Slow small integer division

`http://d.puremagic.com/issues/show_bug.cgi?id=5607`
```
Summary: Slow small integer division
Product: D
Version: D2
Platform: x86
OS/Version: Windows
Status: NEW
Severity: enhancement
Priority: P2
Component: DMD
AssignedTo: nob...@puremagic.com
ReportedBy: bearophile_h...@eml.cc

--- Comment #0 from bearophile_h...@eml.cc 2011-02-17 16:15:32 PST ---
While solving some Project Euler problems with D and C, I have found about five
fold performance difference. I have reduced the code to a small benchmark (that
shows a smaller difference).

Probably the problem comes from %10 and /10 done on uint. DMD uses div, while
GCC uses a known trick for small integer division/modulus. On the web there are
pages that explain how to implement this small integer division optimization
(example: http://libdivide.com/ ).

---------------------------------

Timings, n = 100_000_000:
GCC:  3.13 s
DMD: 11.69 s

dmd -O -release -inline testd.d
gcc -O3 -s testc.c -o testc.exe

32 bit
GCC 4.5.2
DMD 2.052beta

---------------------------------

// D2 code
import std.c.stdio: printf;

int main() {
uint total = 0;
uint i;
for (i = 0; i < 100000000; i++) {
uint n = i;
uint res = n % 10;
n /= 10;
while (n != 0) {
res = (n % 10) + (10 * res);
n /= 10;
}
total += res;
}
printf("%u\n", total); // 461784529
return 0;
}

---------------------------------

// C code
#include "stdio.h"
typedef unsigned long uint;

int main() {
uint total = 0;
uint i;
for (i = 0; i < 100000000; i++) {
uint n = i;
uint res = n % 10;
n /= 10;
while (n != 0) {
res = (n % 10) + (10 * res);
n /= 10;
}
total += res;
}
printf("%u\n", total); // 461784529
return 0;
}

---------------------------------

DMD inner loop:

L1C:    lea    EBX,[EBX*4][EBX]
mov    EAX,ESI
mov    ECX,0Ah
xor    EDX,EDX
div    ECX
test EAX,EAX
mov    ESI,EAX
jne    L1C

---------------------------------

GCC inner loop:

L7:
movl    %ecx, %eax
mull    %esi
leal    (%ebx,%ebx,4), %ebx
shrl    \$3, %edx
leal    (%edx,%edx,4), %eax