zkevm-docs/9-bitwise.markdown

@@ -95,3 +95,26 @@ pub struct BitwiseCircuitConfig<F: Field> {
 
 注：只对Tag不为Nil的行进行LookUp
 
+### ACC计算
+
+应该使用u128.to_be_bytes,即大端序来计算，例如:0x123456789a计算acc
+
+```shell
+---->u128.to_be_bytes()
+---->小端序[u8;16]: 内存地址增长方向：低--------------------->高
+----> [154,120,86,52,18, 0, 0...0, 0]
+----> 即[0x9a,0x78,0x56,0x34,0x12, 0, 0...0, 0]
+---->遍历[u8;16], acc = cur_byte + acc_pre
+---->0x9a785634120000000000000000000000
+```
+
+```shell
+---->u128.to_be_bytes()
+---->大端序[u8;16]：内存地址增长方向：高<---------------------低
+---->[0, 0...18,52,86,120,154]
+---->即[0, 0...0x12,0x34,0x56,0x78,0x9a]
+---->遍历[u8;16], acc = cur_byte + acc_pre
+----> 0x0000000000000000000000123456789a
+```
+
+即u128的大端序的[u8;16]计算acc是所求的数值