SQLITE源码剖析(4)

声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iteye.com/)原创，未经笔者授权，任何人和机构不能转载

/*

** Many people are failing to set -DNDEBUG=1 when compiling SQLite.

** Setting NDEBUG makes the code smaller and run faster.  So the following

** lines are added to automatically set NDEBUG unless the -DSQLITE_DEBUG=1

** option is set.  Thus NDEBUG becomes an opt-in rather than an opt-out

** feature.

*/

// NDEBUG设置能使代码更小，且运行地更快

#if !defined(NDEBUG) && !defined(SQLITE_DEBUG) 

# define NDEBUG 1

#endif

 

/*

** The testcase() macro is used to aid in coverage testing.  When 

** doing coverage testing, the condition inside the argument to

** testcase() must be evaluated both true and false in order to

** get full branch coverage.  The testcase() macro is inserted

** to help ensure adequate test coverage in places where simple

** condition/decision coverage is inadequate.  For example, testcase()

** can be used to make sure boundary values are tested.  For

** bitmask tests, testcase() can be used to make sure each bit

** is significant and used at least once.  On switch statements

** where multiple cases go to the same block of code, testcase()

** can insure that all cases are evaluated.

**

*/

//在覆盖测试时使用testcase()宏

#ifdef SQLITE_COVERAGE_TEST

SQLITE_PRIVATE   void sqlite3Coverage(int);

# define testcase(X)  if( X ){ sqlite3Coverage(__LINE__); }

#else

# define testcase(X)

#endif

 

/*

** The TESTONLY macro is used to enclose variable declarations or

** other bits of code that are needed to support the arguments

** within testcase() and assert() macros.

*/

// TESTONLY将变量声明或需要使用testcase()和assert()宏

//的参数的代码片断包围

#if !defined(NDEBUG) || defined(SQLITE_COVERAGE_TEST)

# define TESTONLY(X)  X

#else

# define TESTONLY(X)

#endif

 

/*

** Sometimes we need a small amount of code such as a variable initialization

** to setup for a later assert() statement.  We do not want this code to

** appear when assert() is disabled.  The following macro is therefore

** used to contain that setup code.  The "VVA" acronym stands for

** "Verification, Validation, and Accreditation".  In other words, the

** code within VVA_ONLY() will only run during verification processes.

*/

//在写一段代码如变量初始化时，需要设置assert()语句进行验证，

//当assert（）被禁止时，我们不希望看到这些代码

// 包括VVA_ONLY()的代码仅在验证后才运行

#ifndef NDEBUG

# define VVA_ONLY(X)  X

#else

# define VVA_ONLY(X)

#endif

 

/*

** ALWAYS和NEVER宏环绕boolean表达式，分别为true或false，

**代码中的这些表达式能被完全忽略,但他们在少数情况下被用于提高SQLITE

**异常恢复能力，使代码自修复。

** The ALWAYS and NEVER macros surround boolean expressions which 

** are intended to always be true or false, respectively.  Such

** expressions could be omitted from the code completely.  But they

** are included in a few cases in order to enhance the resilience

** of SQLite to unexpected behavior - to make the code "self-healing"

** or "ductile" rather than being "brittle" and crashing at the first

** hint of unplanned behavior.

** ALWAYS和NEVER可被用于防御代。当做覆盖测试时，

**ALWAYS和NEVER被硬编码为true和false，

**无法访问的代码，不能算作未经测试的代码。

** In other words, ALWAYS and NEVER are added for defensive code.

**

** When doing coverage testing ALWAYS and NEVER are hard-coded to

** be true and false so that the unreachable code then specify will

** not be counted as untested code.

*/

#if defined(SQLITE_COVERAGE_TEST)

# define ALWAYS(X)      (1)

# define NEVER(X)       (0)

#elif !defined(NDEBUG)

# define ALWAYS(X)      ((X)?1:(assert(0),0))

# define NEVER(X)       ((X)?(assert(0),1):0)

#else

# define ALWAYS(X)      (X)

# define NEVER(X)       (X)

#endif

 

/*

** The macro unlikely() is a hint that surrounds a boolean

** expression that is usually false.  Macro likely() surrounds

** a boolean expression that is usually true.  GCC is able to

** use these hints to generate better code, sometimes.

*/

// 对于包围的boolean表达式，unlikely()为false,likely()为true

// GCC有时可使用这些暗示产生更好的代码。

#if defined(__GNUC__) && 0

# define likely(X)    __builtin_expect((X),1)

# define unlikely(X)  __builtin_expect((X),0)

#else

# define likely(X)    !!(X)

# define unlikely(X)  !!(X)

#endif