Update README.md

testing/README.md

@@ -10,6 +10,7 @@
 - 1.1.2 basic concept
   - To operate several calculation for fixed-point numebr type casting is essential.
   - Correct type conversion is very important in order to accurately calculate and avoid missing bits.
+  - in iteration2, with using shift operation can create a variety of functions that perform differently under different conditions.
 - 1.1.3 concept of fixed-point number
   - ![image](/uploads/0ae109d4300d11722c53531d1a9615ac/image.png)
     - a. data types in computer langauge always have fixed length 
@@ -23,7 +24,7 @@
 ## 2. overall description
 ### - 2.1 product functions
 - 2.1.1 list of fuctions
-  - 2.1.1.1 stpe 1
+  - 2.1.1.1 iteration 1
     - a. add
       ~~~
       #define fx_add(a, b) ((a)+(b))
@@ -84,3 +85,34 @@
       - first convert fixed number to double
       - second do sqrt operation with math library
       - thrid conver result calculated by second step to double and return result
+  - 2.1.1.2 iteration 2
+    - a. mul
+      ~~~
+      ((fa * fb) >> FX32_QNUM ) 
+      ~~~
+      - fuction that multiplies fa and fb and divides it by 2^32
+    - b. mul1
+      ~~~
+      ((fa>>16) * fb)>>16)
+      ~~~
+      - Same as fx32_mul, the same fuction as fa*fb>>32, first multiply fa/2^16 and fb, and divide the remaining 2^16
+    - c. mul2
+      ~~~
+      (((fa>>8)*(fb>>8))>>16)
+      ~~~
+      - Same as above, the same fuction as fa*fb>>32, first multiply fa/2^8, fb/2^8, and divide the remaining 2^16
+    - d. div
+      ~~~
+      ((((fixed64)(fa) << FX32_QNUM) /(fb))) 
+      ~~~
+      - fuction that multiplies fa by 2^32 and divides fb.
+    - e. div1
+      ~~~
+      ((((fa)<<16)/(fb))<<16)
+      ~~~
+      - Same as above, it has the same fuction as (fa<<32)/fb. First, fa is multiplied by 2^16 and divided by fb, and then the remaining 2^16 is multiplied
+    - f. div2
+      ~~~
+      ((((fa)<<24)/(fb))<<8)
+      ~~~
+      - same as above, it has the same fuction as (fa<<32)/fb. First, fa is multiplied by 2^24, divided by fb, and then the remaining 2^8 is multiplied.
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