STM32G031で二進固定小数点で遊ぶ2(四則演算)

x 動作確認済み2022/6/10 7:42

x OBでGPIOがわかる人むけ

目的　
適当にごもごもするから四則演算をまともに
した時は、ないが今後の為

二進固定小数点　2ビット　0.25 ←→ 1/4　の話

二進固定小数点の時は、とりあえず4倍するんや!!
そうすると精度が4倍になり0,.25,.5,.75がねじ込めるるんや!!

足し算と引き算は、そのまま

A + B = C

A - B = C

例

1.25 + 1.50 = 2.75

2.75 - 1.50 = 1.25

足し算

1.25 + 1.50 = 2.75

1.25 → (1 * 4)+(1) = 5(101B)
1.50 → (1 * 4)+(2) = 6(110B)

101B + 110B = 11(1011B)

2.75 →　(2 * 4)+(3) = 11(1011B)

引き算

2.75 - 1.50 = 1.25

2.75 →　(2 * 4)+(3) = 11(1011B)
1.50 → (1 * 4)+(2) = 6 (110B)

1011B - 110B = 5(101B)

1.25 → (1 * 4)+(1) = 5(101B)

掛け算は、小数点分右にシフト

小数点N

A * B = C

C >> N

2.0 * 1.5 = 3.0

2.0 →　(2 * 4) + (0) = 8
1.5 →　(1 * 4) + (2) = 6

8 * 6 = 48

48 /2 = 24
24 /2 = 12

12 →　( 3 * 4 )+(0)

3.0

割り算

割り算は、小数点分左にシフトして割る

小数点N

( A << N ) / B = C

3.0 / 1.5 = 2.0

3.0 →　(3 * 4) + (0) = 12
1.5 →　(1 * 4) + (2) = 6

(12 * 4) / 6 = 8
48 / 6 = 8

8 →　(2 * 4) + (0)

2.0

#include <stdio.h>
int main(void){
    
    
    int a,b,c;
    char *f4[]={".0",".25",".5",".75"};
    
    
    //1.25 + 1.50 = 2.75
    
    a = (1<<2)+(1); //1.25
    b = (1<<2)+(2); //1.5
    c = a+b;
    printf("%d",c>>2);
    printf("%s\r\n",f4[c & 0x03]);
    
    
    //2.75 - 1.50 = 1.25
    
    a = (2<<2)+(3); //2.75
    b = (1<<2)+(2); //1.25
    c = a-b;
    printf("%d",c>>2);
    printf("%s\r\n",f4[c & 0x03]);
    
    
    //2.0 * 1.5 = 3.0
    
    a=(2<<2)+(0); //2.0
    b=(1<<2)+(2); //1.5
    c = a*b;
    c = c>>2;
    printf("%d",c>>2);
    printf("%s\r\n",f4[c & 0x03]);
    
    
    //3.0 / 1.5 = 2.0

    a = (3<<2)+(0); //3.0
    b = (1<<2)+(2); //1.5
    c=(a<<2)/b;
    printf("%d",c>>2);
    printf("%s\r\n",f4[c & 0x03]);
    
}

2.75
1.25
3.0
2.0

//SER_f4_4_031_1


#include <Arduino.h>
#include <HardwareSerial.h>


//初期化
void setup() {

  delay(3000); //not delete

  Serial.setTx(PA2_ALT1);
  Serial.setHalfDuplex();
  Serial.begin(9600);


}//setup

int a,b,c;
char *f4[]={".0",".25",".5",".75"};

//メインループ
void loop() {

    //1.25 + 1.50 = 2.75

    Serial.println("1.25 + 1.50");
    a = (1<<2)+(1); //1.25
    b = (1<<2)+(2); //1.5
    c = a+b;
    Serial.print(c>>2);
    Serial.println(f4[c & 0x03]);
    
    
    //2.75 - 1.50 = 1.25

    Serial.println("2.75 - 1.50");
    a = (2<<2)+(3); //2.75
    b = (1<<2)+(2); //1.25
    c = a-b;
    Serial.print(c>>2);
    Serial.println(f4[c & 0x03]);
    
    
    //2.0 * 1.5 = 3.0

    Serial.println("2.0 * 1.5");
    a=(2<<2)+(0); //2.0
    b=(1<<2)+(2); //1.5
    c = a*b;
    c = c>>2;
    Serial.print(c>>2);
    Serial.println(f4[c & 0x03]);
    
    
    //3.0 / 1.5 = 2.0

    Serial.println("3.0 / 1.5");
    a = (3<<2)+(0); //3.0
    b = (1<<2)+(2); //1.5
    c=(a<<2)/b;
    Serial.print(c>>2);
    Serial.println(f4[c & 0x03]);


  delay(4000);

}//loop