SQLITE源码剖析(4)

deepfuture

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_TESTSQLITE_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