On Fri, 8 Dec 2017 14:26:43 +0100, "wolfgang kern"    
   wrote:   
   >...   
   >you found a max.value ?  OK, me once too!   
   >...   
   Yes, but you use the shifted version here.  I used the one that gives   
   a 32 bit quotient in edx without shifting.   
      
   I wrote a ROSASM program that poped up a dialog where I could input   
   the divisor, and it calculated the reciprocal and immediately went   
   into the loop and printed the first number that gives a bad result.   
   And there was a x+1 checkbox to tell if the input should be increased   
   by 1.   
      
   Here is what some of them gave:   
      
   Divisor Reciproal  hightest number   
      3    0x55555555 4296967294 x+1 on   
      5    0x33333333 4294967294 x+1 on   
     10    0x1999999A 1073741828 x+1 off   
     15    0x11111111 4294967294 x+1 on   
      
   >here is a copy of what I tried for 32 bit after Terje showed me the   
   >error with my 0x1999999A reciprocal some years ago.   
   >(haven't checked if this can be modified for 64 bit):   
   >..   
   >BIN2DEC:   
   >.ALIGN 64   
   >  mov eax,0xffffffff   ;max. num test /others tested as well   
   >  mov ebx,0xcccccccd   ;2^35/10   
   >  mov edi,BUFFER+10    ;point to end because stored backwards   
   >  mov [edi],byte 0     ;Z-terminator   
   >.ALIGN 4   
   >L1:   
   >  mov ecx,eax          ;copy initial value or last quotient   
   >  mul ebx              ;divide   
   >  dec edi              ;goes backward   
   >  shr edx,3            ;-> 2^32   
   >  lea esi,[edx+edx*8]  ; *9  (SUB ecx,edx*10)   
   >  sub ecx,edx          ;-*1   
   >  sub ecx,esi          ;-*9   
   >  mov eax,edx          ;prepare for next   
   >  or  ecx,+30h         ;   
   >  test edx,edx         ;only until nothing more   
   >  mov [edi],cl         ;   
   > jnz L1                ;   
   > ret                   ;edi points to first character (MSD) yet   
   >.ALIGN 64              ;must be at least one cache line away from code   
   >BUFFER: dup 11 ?       ;ASCII-Z num w/o leading Zeros   
   >-----------   
   Thanks, I will take a closer look, if a can use it somehow!   
   --   
   aen   
      
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