如何计算事业部提醒在SPARC大会？ [英] How to calculate division reminder in SPARC Assembly?

问题描述

下面是伪code的计算两个正整数除法。
HR寄存器保存的提醒，和LR可以节省股息。 （并最终节省了根）
不过，我认为这个算法有一定的问题。
因为这种算法有时不恢复subtracion。（司是一个延续减法。）
例如 6/3（0110/011）
该算法减-3一次。 （当我们计算这个师的手，这种情况永远不会发生）
因此，我认为这个算法有一定的问题。
难道你不同意我的观点？ 如何计算事业部提醒在大会？

 对于i = 1到num_of_bits做
（HR LR）＆LT;＆LT; 1
如果（HR＆GT; = 0），则
   HR = HR  -  DIVISOR
其他
   HR = HR + DIVISOR
ENDIF
如果（HR大于0），那么LR（LSB）= 1 ENDIF
ENDFOR
 

解决方案

我不说话SPARC ASM，但我不说话C.下面是一个简单的实现算法的16/8 = 8,8师：

 的#include＆LT; stdio.h中＆GT;

的typedef unsigned char型UINT8;
的typedef无符号整型单元;

INT u8div（UINT8 * dividendh，UINT8 * dividendl，UINT8除数）
{
  INT I;

  如果（* dividendh＆GT; =除数）
    返回0; // 溢出

  对于（i = 0; I＆LT; 8;我++）
  {
    如果（* dividendh＆GT; = 0x80的）
    {
      * dividendh =（* dividendh＆LT;＆LT; 1）| （* dividendl＆GT;＆GT;（8  -  1））;
      * dividendl＆其中;＆其中; = 1;

      * dividendh  -  =除数;
      * dividendl | = 1;
    }
    其他
    {
      * dividendh =（* dividendh＆LT;＆LT; 1）| （* dividendl＆GT;＆GT;（8  -  1））;
      * dividendl＆其中;＆其中; = 1;

      如果（* dividendh＆GT; =除数）
      {
        * dividendh  -  =除数;
        * dividendl | = 1;
      }
    }
  }

  返回1;
}

INT u8div2（UINT8 * dividendh，UINT8 * dividendl，UINT8除数）
{
  UINT分红=（* dividendh＆LT;＆LT; 8）| * dividendl;

  如果（* dividendh＆GT; =除数）
    返回0; // 溢出

  * dividendl =股息/除数;
  * dividendh =股息％除数;

  返回1;
}

INT主要（无效）
{
  UINT dividendh，dividendl，除数;

  为（dividendh = 0; dividendh＆其中; = 0xFF的; dividendh ++）
    为（dividendl = 0; dividendl＆其中; = 0xFF的; dividendl ++）
      对于（除数= 0;除数＆LT; = 0xFF的;除数++）
      {
        UINT8 DIVH = dividendh，DIVL = dividendl，divr =除数;
        UINT8 divh2 = dividendh，divl2 = dividendl;

        的printf（为0x％04X /为0x％02X =，（DIVH＆LT;＆LT; 8）| DIVL，divr）;

        如果（u8div（安培; DIVH，和放大器; DIVL，divr））
          的printf（0X％02X.0x％02X，DIVL，DIVH）;
        其他
          的printf（OVF）;

        的printf（）;

        如果（u8div2（安培; divh2，和放大器; divl2，divr））
          的printf（0X％02X.0x％02X，divl2，divh2）;
        其他
          的printf（OVF）;

        如果（（DIVL！= divl2）||（DIVH！= divh2））
          的printf（犯错）;如果u8div（）计算结果不正确//错误将被打印

        的printf（\ N）;
      }

  返回0;
}
 

Here is the pseudo code which computes division of two positive integers.
HR register saves reminder, and LR saves dividend. (and eventually saves root)
However I think this algorithm has some problem.
Because this algorithm sometimes don't recover subtracion.(Division is a continuation of subtraction.)
For example 6 / 3 (0110 / 011)
This algorithm subtract -3 one more time. (This situation never occur when we calculate this division by hand)
So I think this algorithm has some problem.
Don't you agree with me? How to calculate division reminder in Assembly?

for i = 1 to num_of_bits do
(HR LR) << 1
if (HR >= 0) then
   HR = HR - DIVISOR
else
   HR = HR + DIVISOR
endif
if (HR > 0) then LR(lsb) = 1 endif
endfor

解决方案

I don't speak SPARC asm, but I do speak C. Here's a sample implementation of the algorithm for 16/8=8,8 division:

#include <stdio.h>

typedef unsigned char uint8;
typedef unsigned int uint;

int u8div(uint8* dividendh, uint8* dividendl, uint8 divisor)
{
  int i;

  if (*dividendh >= divisor)
    return 0; // overflow

  for (i = 0; i < 8; i++)
  {
    if (*dividendh >= 0x80)
    {
      *dividendh = (*dividendh << 1) | (*dividendl >> (8 - 1));
      *dividendl <<= 1;

      *dividendh -= divisor;
      *dividendl |= 1;
    }
    else
    {
      *dividendh = (*dividendh << 1) | (*dividendl >> (8 - 1));
      *dividendl <<= 1;

      if (*dividendh >= divisor)
      {
        *dividendh -= divisor;
        *dividendl |= 1;
      }
    }
  }

  return 1;
}

int u8div2(uint8* dividendh, uint8* dividendl, uint8 divisor)
{
  uint dividend = (*dividendh << 8) | *dividendl;

  if (*dividendh >= divisor)
    return 0; // overflow

  *dividendl = dividend / divisor;
  *dividendh = dividend % divisor;

  return 1;
}

int main(void)
{
  uint dividendh, dividendl, divisor;

  for (dividendh = 0; dividendh <= 0xFF; dividendh++)
    for (dividendl = 0; dividendl <= 0xFF; dividendl++)
      for (divisor = 0; divisor <= 0xFF; divisor++)
      {
        uint8 divh = dividendh, divl = dividendl, divr = divisor;
        uint8 divh2 = dividendh, divl2 = dividendl;

        printf("0x%04X/0x%02X=", (divh << 8) | divl, divr);

        if (u8div(&divh, &divl, divr))
          printf("0x%02X.0x%02X", divl, divh);
        else
          printf("ovf");

        printf(" ");

        if (u8div2(&divh2, &divl2, divr))
          printf("0x%02X.0x%02X", divl2, divh2);
        else
          printf("ovf");

        if ((divl != divl2) || (divh != divh2))
          printf(" err"); // "err" will be printed if u8div() computes incorrect result

        printf("\n");
      }

  return 0;
}

这篇关于如何计算事业部提醒在SPARC大会？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！