Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
1.2k views
in Technique[技术] by (71.8m points)

c - gcc 7.3 128-bit unsigned integer operation

I'm confused with the usage of 128-bit integer. Please look at the test code:

uint128_t test_data = 0x00000000FFFFFFFF0101010101010101;
uint64_t test_data_h = test_data  >> 64;
uint64_t test_data_l = test_data ;
printf("test_data 0x %016llx %016llx
", test_data_h, test_data_l);

I expect the test_data_h to be 0x00000000FFFFFFFF, but the result is :

test data 0x 0000000000000000 0101010101010101

Why is this?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

Many compilers do not support 128 bit constants.

Instead

// uint128_t test_data = 0x00000000FFFFFFFF0101010101010101;
uint128_t test_data = (((uint128_t) 0x00000000FFFFFFFF) << 64) | 0x0101010101010101;

Tip: enable all compiler warnings.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...