lmathlib.c源码解析

Lua通过标准库实现了核心之外的功能，如math库，I/O库等。

标准库由C语言函数实现，提供给Lua程序使用。Lua程序与C函数通过虚拟栈交互。Lua将参数压入栈中，C函数从栈中获取参数，并将结果压入栈中，C函数返回入栈的结果数量。C函数无需在压入结果前清空栈，Lua会在函数执行完成后从栈中获取结果并自动清空结果下的内容。

/*** $Id: lmathlib.c,v 1.67.1.1 2007/12/27 13:02:25 roberto Exp $** Standard mathematical library** See Copyright Notice in lua.h*/#include <stdlib.h>#include <math.h>#define lmathlib_c#define LUA_LIB#include "lua.h"#include "lauxlib.h"#include "lualib.h"#undef PI#define PI (3.14159265358979323846)#define RADIANS_PER_DEGREE (PI/180.0)//lua将待转换的数字放入到lua栈，然后luaL_checknumber判断能否转换为数字，//能的话返回给fabs进行处理，然后将处理的结果push到lua栈中static int math_abs (lua_State *L) {  lua_pushnumber(L, fabs(luaL_checknumber(L, 1)));  return 1;}static int math_sin (lua_State *L) {  lua_pushnumber(L, sin(luaL_checknumber(L, 1)));  return 1;}static int math_sinh (lua_State *L) {  lua_pushnumber(L, sinh(luaL_checknumber(L, 1)));  return 1;}static int math_cos (lua_State *L) {  lua_pushnumber(L, cos(luaL_checknumber(L, 1)));  return 1;}static int math_cosh (lua_State *L) {  lua_pushnumber(L, cosh(luaL_checknumber(L, 1)));  return 1;}static int math_tan (lua_State *L) {  lua_pushnumber(L, tan(luaL_checknumber(L, 1)));  return 1;}static int math_tanh (lua_State *L) {  lua_pushnumber(L, tanh(luaL_checknumber(L, 1)));  return 1;}static int math_asin (lua_State *L) {  lua_pushnumber(L, asin(luaL_checknumber(L, 1)));  return 1;}static int math_acos (lua_State *L) {  lua_pushnumber(L, acos(luaL_checknumber(L, 1)));  return 1;}static int math_atan (lua_State *L) {  lua_pushnumber(L, atan(luaL_checknumber(L, 1)));  return 1;}static int math_atan2 (lua_State *L) {  lua_pushnumber(L, atan2(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_ceil (lua_State *L) {  lua_pushnumber(L, ceil(luaL_checknumber(L, 1)));  return 1;}static int math_floor (lua_State *L) {  lua_pushnumber(L, floor(luaL_checknumber(L, 1)));  return 1;}static int math_fmod (lua_State *L) {  lua_pushnumber(L, fmod(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_modf (lua_State *L) {  double ip;  double fp = modf(luaL_checknumber(L, 1), &ip);  lua_pushnumber(L, ip);  lua_pushnumber(L, fp);  return 2;}static int math_sqrt (lua_State *L) {  lua_pushnumber(L, sqrt(luaL_checknumber(L, 1)));  return 1;}static int math_pow (lua_State *L) {  lua_pushnumber(L, pow(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_log (lua_State *L) {  lua_pushnumber(L, log(luaL_checknumber(L, 1)));  return 1;}static int math_log10 (lua_State *L) {  lua_pushnumber(L, log10(luaL_checknumber(L, 1)));  return 1;}static int math_exp (lua_State *L) {  lua_pushnumber(L, exp(luaL_checknumber(L, 1)));  return 1;}static int math_deg (lua_State *L) {  lua_pushnumber(L, luaL_checknumber(L, 1)/RADIANS_PER_DEGREE);  return 1;}static int math_rad (lua_State *L) {  lua_pushnumber(L, luaL_checknumber(L, 1)*RADIANS_PER_DEGREE);  return 1;}static int math_frexp (lua_State *L) {  int e;  lua_pushnumber(L, frexp(luaL_checknumber(L, 1), &e));  lua_pushinteger(L, e);  return 2;}static int math_ldexp (lua_State *L) {  lua_pushnumber(L, ldexp(luaL_checknumber(L, 1), luaL_checkint(L, 2)));  return 1;}static int math_min (lua_State *L) {  int n = lua_gettop(L);  /* number of arguments */  lua_Number dmin = luaL_checknumber(L, 1);  int i;  for (i=2; i<=n; i++) {    lua_Number d = luaL_checknumber(L, i);    if (d < dmin)      dmin = d;  }  lua_pushnumber(L, dmin);  return 1;}static int math_max (lua_State *L) {  int n = lua_gettop(L);  /* number of arguments */  lua_Number dmax = luaL_checknumber(L, 1);  int i;  for (i=2; i<=n; i++) {    lua_Number d = luaL_checknumber(L, i);    if (d > dmax)      dmax = d;  }  lua_pushnumber(L, dmax);  return 1;}static int math_random (lua_State *L) {  /* the `%' avoids the (rare) case of r==1, and is needed also because on     some systems (SunOS!) `rand()' may return a value larger than RAND_MAX */  lua_Number r = (lua_Number)(rand()%RAND_MAX) / (lua_Number)RAND_MAX;  switch (lua_gettop(L)) {  /* check number of arguments */    case 0: {  /* no arguments */      lua_pushnumber(L, r);  /* Number between 0 and 1 */      break;    }    case 1: {  /* only upper limit */      int u = luaL_checkint(L, 1);      luaL_argcheck(L, 1<=u, 1, "interval is empty");      lua_pushnumber(L, floor(r*u)+1);  /* int between 1 and `u' */      break;    }    case 2: {  /* lower and upper limits */      int l = luaL_checkint(L, 1);      int u = luaL_checkint(L, 2);      luaL_argcheck(L, l<=u, 2, "interval is empty");      lua_pushnumber(L, floor(r*(u-l+1))+l);  /* int between `l' and `u' */      break;    }    default: return luaL_error(L, "wrong number of arguments");  }  return 1;}static int math_randomseed (lua_State *L) {  srand(luaL_checkint(L, 1));  return 0;}static const luaL_Reg mathlib[] = {  {"abs",   math_abs},  {"acos",  math_acos},  {"asin",  math_asin},  {"atan2", math_atan2},  {"atan",  math_atan},  {"ceil",  math_ceil},  {"cosh",   math_cosh},  {"cos",   math_cos},  {"deg",   math_deg},  {"exp",   math_exp},  {"floor", math_floor},  {"fmod",   math_fmod},  {"frexp", math_frexp},  {"ldexp", math_ldexp},  {"log10", math_log10},  {"log",   math_log},  {"max",   math_max},  {"min",   math_min},  {"modf",   math_modf},  {"pow",   math_pow},  {"rad",   math_rad},  {"random",     math_random},  {"randomseed", math_randomseed},  {"sinh",   math_sinh},  {"sin",   math_sin},  {"sqrt",  math_sqrt},  {"tanh",   math_tanh},  {"tan",   math_tan},  {NULL, NULL}};//当在Lua程序中，调用require("math")时，就会调用下面的luaopen_math函数，来注册函数库//lua5.1 之中有一个luaL_register,用于把luaL_Reg 数组中的所有函数注册到lua中。但在lua5.2中已经不支持这一函数了//lua_setfield设置lua栈中的值//HUGE_VAL是C语言在<error.h>定义的一个非常大的double正数。LUALIB_API int luaopen_math (lua_State *L) {  luaL_register(L, LUA_MATHLIBNAME, mathlib);  lua_pushnumber(L, PI);  lua_setfield(L, -2, "pi");  lua_pushnumber(L, HUGE_VAL);  lua_setfield(L, -2, "huge");#if defined(LUA_COMPAT_MOD)  lua_getfield(L, -1, "fmod");  lua_setfield(L, -2, "mod");#endif  return 1;}
结构体实例mathlib中保存了lua函数库所有的接口，结构体luaL_Reg在lauxlib.h中的定义的：typedef struct luaL_Reg {const char *name;lua_CFunction func;} luaL_Reg;这里的函数类型lua_CFunction在lua.h中定义的：typedef int (*lua_CFunction) (lua_State *L);所有用C实现的Lua函数，都是必须是这种类型，即一个lua_State的参数，返回值为int。
HUGE_VAL是C语言在<error.h>定义的一个非常大的double正数。