SQLITE源码剖析(4)

q666123

　　声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iyunv.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