使用 Java 中的位移位获取存储的数字

Question

I'm having trouble trying to reverse engineer this section of code; I need to be able to get x, y, z from l would anyone be able to point me in the right direction. Thanks

 int l = ((X << 20) + (Y << 19) + Z);

The ranges are as follows

X = 0 - 4095
Y = 0 - 1
Z = 0 - 384,794

Answer 1

X being 0-4095 = 12 bits

Y being 0-1 = 1 bit

Z being 0-384794 = 19 bits

Java integers are 32 bit, so starting from 0:

int l = 0000 0000 0000 0000 0000 0000 0000 0000

+ X << 20 = the value of X, moved 20 places to the right. So:

int l = XXXX XXXX XXXX 0000 0000 0000 0000 0000

+ Y << 19 = the value of Y, moved 19 places to the right. So:

int l = XXXX XXXX XXXX Y000 0000 0000 0000 0000

+ Z = the value of Z, moved 0 places. So:

int l = XXXX XXXX XXXX YZZZ ZZZZ ZZZZ ZZZZ ZZZZ

Since no bits are ever overwritten, we can recover them:

int x = l >> 20 & 0xFFF;   //reverse the shifting (by 20), then isolate the X bits (0xFFF = 12 bits set to 1, equal to 4095)
int y = l >> 19 & 0x1;     //reverse the shifting (by 19), then isolate the Y bit (0x1 = 1 bit set to 1, equal to 1)
int z = l & 0x7FFFF;       //no shifting to reverse, but we still isolate the Z bits (0x7FFFF = 19 bits set to 1, equal to 524287)