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Can XMM registers be used to do any 128 bit integer math? [duplicate]

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问题 This question already has an answer here : Is it possible to use SSE and SSE2 to make a 128-bit wide integer? (1 answer) Closed 2 years ago . My impression is definitely not but perhaps there is a clever trick? Thanks. 回答1: Not directly, but there are 64 bit arithmetic operations which can be easily combined to perform 128 bit (or greater) precision. 回答2: The xmm registers can do arithmetics on 8, 16, 32 and 64 bit integers. It doesn't produce a carry flag so you can't extend the precision

rails3 bigint primary key

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问题 I would like to create a bigint (or string or whatever that is not int ) typed primary key field under Rails 3. I have a given structure of data, for example: things ------ id bigint primary_key name char(32) The approach I'm currently trying to push: create_table :things, :id => false do |t| # That prevents the creation of (id int) PK t.integer :id, :limit => 8 # That makes the column type bigint t.string :name, :limit => 32 t.primary_key :id # This is perfectly ignored :-( end The column

SQL Server varbinary bigint with BitConverter.ToInt64 values are different

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问题 I save my long value in a SQL Server table as varbinary(max) : var savedValue = BitConverter.GetBytes(longValue); Now I need to work with that value in T-SQL query, but when I trying to get value: select cast(Value as bigint) from dbo.MyValues It returns different number value. For example if I saved -8588797048854775808 in .NET, in T-SQL I get 33802181122903688 Please tell me what's the problem? Have that issue any solution? 回答1: Casting from varbinary to bigint (and back) uses network byte

How to use long id in Rails applications?

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How can I change the (default) type for ActiveRecord's IDs? int is not long enough, I would prefer long. I was surprised that there is no :long for the migrations - does one just use some decimal? Credits to http://moeffju.net/blog/using-bigint-columns-in-rails-migrations class CreateDemo < ActiveRecord::Migration def self.up create_table :demo, :id => false do |t| t.integer :id, :limit => 8 end end end See the option :id => false which disables the automatic creation of the id field The t.integer :id, :limit => 8 line will produce a 64 bit integer field To set the default primary key column

PostgreSQL 修改字段类型从int到bigint

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由于现在pg的版本，修改int到bigint仍然需要rewrite表，会导致表阻塞，无法使用。但可以考虑其他方式来做。此问题是排查现网pg使用序列的情况时遇到的。由于int的最大值只有21亿左右，而且自增列多为主键，当达到最大值时，数据就会无法插入。一般情况是修改类型为bigint，但直接做会锁表，影响现网使用。这里分两块来看： 1、分区表（修改序列）：对于分区表可以直接修改序列为循环形式，而且最大值设置为int的最大值，因为单个分区表很少会将int值用完。 alter sequence seq_name MAXVALUE 2147483647 CYCLE; 注意这里适用于按日或按月分区的表，对于hash分区表，只能修改字段类型。 2、非分区表（修改为bigint）由于创建表时，可能使用的是serial，所以此时就需要新建一个序列，不然字段id在删除时，之前的序列也会跟着一同被删除。下面的步骤中要注意，添加主键约束部分，如果new_id上没有not null约束，则此时会进行全表扫描检查有无not null的记录。虽然pg检查记录是否为not null的操作比较快，但这一步还是会锁较长时间（看记录数多少而定）。 alter table table_name add column new_id bigint ; -- -循环更新new_id do language

C++ 128/256-bit fixed size integer types

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问题 I was wondering if any fellow SO's could recommend a good light-weight fixed size integer type (128-bit or even 256-bit, possibly even template parametrized) library. I've had a look at GMP and co, they care great, yet are a bit too large for my purposes, I'm interested in simple header only solutions at this point. Performance is important and the target architecture will be x86 and x86-64, also a reasonable license (aka nothing GPL or LGPL). 回答1: The Boost library has data types as part of

Big integer in C or C++ [closed]

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I was working on a factorial program, and the program didn't work when trying to find the factorial of 1000. I think big integers are the solution; how do they work? (In either C or C++) GMP can do bigint operations for both C and C++. The documentation on that site is a good introduction, if you use the C++ classes they behave almost exactly like built-in primitive types. Leonidas Look for the GMP. See the other question regarding this topic: Handling very large Integers C++ Big Integer 来源： https://stackoverflow.com/questions/4827538/big-integer-in-c-or-c

A good and basic implementation of BigInt class in C++ [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . I'm looking for a good and basic BigInt class in C++, I find a lot of implementation but most of the time, it's complex implementation for crypto library... By basic, I mean BigInt can deal with BigInt, long long and strings with operator overloading. If I had time, I had done myself but I do not have time to

mysql存储过程中使用临时表

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当工作在很大的表上时，您可能偶尔需要运行很多查询获得一个大量数据的小的子集，不是对整个表运行这些查询，而是让MySQL每次找出所需的少数记录，将记录选择到一个临时表可能更快些，然后多这些表运行查询。　　创建临时表很容易，给正常的CREATE TABLE语句加上TEMPORARY关键字: 　　CREATE TEMPORARY TABLE tmp_table ( 　　name VARCHAR(10) NOT NULL, 　　value INTEGER NOT NULL 　　) 　　临时表将在您连接MySQL期间存在。当您断开时，MySQL将自动删除表并释放所用的空间。当然您能够在仍然连接的时候删除表并释放空间。　　DROP TABLE tmp_table 　　假如在您创建名为tmp_table临时表时名为tmp_table的表在数据库中已存在，临时表将有必要屏蔽(隐藏)非临时表 tmp_table。　　假如您声明临时表是个HEAP表，MySQL也允许您指定在内存中创建他: 　　CREATE TEMPORARY TABLE tmp_table ( 　　name VARCHAR(10) NOT NULL, 　　value INTEGER NOT NULL 　　) TYPE = HEAP 　　因为HEAP表存储在内存中，您对他运行的查询可能比磁盘上的临时表快些。然而

What is the equivalent of bigint in C#?

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问题 What I am supposed to use when handling a value in C#, which is bigint for an SQL Server database? 回答1: That corresponds to the long (or Int64 ), a 64-bit integer. Although if the number from the database happens to be small enough, and you accidentally use an Int32, etc., you'll be fine. But the Int64 will definitely hold it. And the error you get if you use something smaller and the full size is needed? A stack overflow! Yay! 回答2: Int64 maps directly to BigInt . Source 回答3: I just had a

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