漫话Redis源码之一百一十七

这里是编码相关的函数，有很多magic number, 一般看函数的功能和用途即可：

/* we assume IEEE 754 internal format for single and double precision floats. */
void mp_encode_double(lua_State *L, mp_buf *buf, double d) {
    unsigned char b[9];
    float f = d;

    assert(sizeof(f) == 4 && sizeof(d) == 8);
    if (d == (double)f) {
        b[0] = 0xca;    /* float IEEE 754 */
        memcpy(b+1,&f,4);
        memrevifle(b+1,4);
        mp_buf_append(L,buf,b,5);
    } else if (sizeof(d) == 8) {
        b[0] = 0xcb;    /* double IEEE 754 */
        memcpy(b+1,&d,8);
        memrevifle(b+1,8);
        mp_buf_append(L,buf,b,9);
    }
}

void mp_encode_int(lua_State *L, mp_buf *buf, int64_t n) {
    unsigned char b[9];
    int enclen;

    if (n >= 0) {
        if (n <= 127) {
            b[0] = n & 0x7f;    /* positive fixnum */
            enclen = 1;
        } else if (n <= 0xff) {
            b[0] = 0xcc;        /* uint 8 */
            b[1] = n & 0xff;
            enclen = 2;
        } else if (n <= 0xffff) {
            b[0] = 0xcd;        /* uint 16 */
            b[1] = (n & 0xff00) >> 8;
            b[2] = n & 0xff;
            enclen = 3;
        } else if (n <= 0xffffffffLL) {
            b[0] = 0xce;        /* uint 32 */
            b[1] = (n & 0xff000000) >> 24;
            b[2] = (n & 0xff0000) >> 16;
            b[3] = (n & 0xff00) >> 8;
            b[4] = n & 0xff;
            enclen = 5;
        } else {
            b[0] = 0xcf;        /* uint 64 */
            b[1] = (n & 0xff00000000000000LL) >> 56;
            b[2] = (n & 0xff000000000000LL) >> 48;
            b[3] = (n & 0xff0000000000LL) >> 40;
            b[4] = (n & 0xff00000000LL) >> 32;
            b[5] = (n & 0xff000000) >> 24;
            b[6] = (n & 0xff0000) >> 16;
            b[7] = (n & 0xff00) >> 8;
            b[8] = n & 0xff;
            enclen = 9;
        }
    } else {
        if (n >= -32) {
            b[0] = ((signed char)n);   /* negative fixnum */
            enclen = 1;
        } else if (n >= -128) {
            b[0] = 0xd0;        /* int 8 */
            b[1] = n & 0xff;
            enclen = 2;
        } else if (n >= -32768) {
            b[0] = 0xd1;        /* int 16 */
            b[1] = (n & 0xff00) >> 8;
            b[2] = n & 0xff;
            enclen = 3;
        } else if (n >= -2147483648LL) {
            b[0] = 0xd2;        /* int 32 */
            b[1] = (n & 0xff000000) >> 24;
            b[2] = (n & 0xff0000) >> 16;
            b[3] = (n & 0xff00) >> 8;
            b[4] = n & 0xff;
            enclen = 5;
        } else {
            b[0] = 0xd3;        /* int 64 */
            b[1] = (n & 0xff00000000000000LL) >> 56;
            b[2] = (n & 0xff000000000000LL) >> 48;
            b[3] = (n & 0xff0000000000LL) >> 40;
            b[4] = (n & 0xff00000000LL) >> 32;
            b[5] = (n & 0xff000000) >> 24;
            b[6] = (n & 0xff0000) >> 16;
            b[7] = (n & 0xff00) >> 8;
            b[8] = n & 0xff;
            enclen = 9;
        }
    }
    mp_buf_append(L,buf,b,enclen);
}

void mp_encode_array(lua_State *L, mp_buf *buf, int64_t n) {
    unsigned char b[5];
    int enclen;

    if (n <= 15) {
        b[0] = 0x90 | (n & 0xf);    /* fix array */
        enclen = 1;
    } else if (n <= 65535) {
        b[0] = 0xdc;                /* array 16 */
        b[1] = (n & 0xff00) >> 8;
        b[2] = n & 0xff;
        enclen = 3;
    } else {
        b[0] = 0xdd;                /* array 32 */
        b[1] = (n & 0xff000000) >> 24;
        b[2] = (n & 0xff0000) >> 16;
        b[3] = (n & 0xff00) >> 8;
        b[4] = n & 0xff;
        enclen = 5;
    }
    mp_buf_append(L,buf,b,enclen);
}

void mp_encode_map(lua_State *L, mp_buf *buf, int64_t n) {
    unsigned char b[5];
    int enclen;

    if (n <= 15) {
        b[0] = 0x80 | (n & 0xf);    /* fix map */
        enclen = 1;
    } else if (n <= 65535) {
        b[0] = 0xde;                /* map 16 */
        b[1] = (n & 0xff00) >> 8;
        b[2] = n & 0xff;
        enclen = 3;
    } else {
        b[0] = 0xdf;                /* map 32 */
        b[1] = (n & 0xff000000) >> 24;
        b[2] = (n & 0xff0000) >> 16;
        b[3] = (n & 0xff00) >> 8;
        b[4] = n & 0xff;
        enclen = 5;
    }
    mp_buf_append(L,buf,b,enclen);
}

/* --------------------------- Lua types encoding --------------------------- */

void mp_encode_lua_string(lua_State *L, mp_buf *buf) {
    size_t len;
    const char *s;

    s = lua_tolstring(L,-1,&len);
    mp_encode_bytes(L,buf,(const unsigned char*)s,len);
}

void mp_encode_lua_bool(lua_State *L, mp_buf *buf) {
    unsigned char b = lua_toboolean(L,-1) ? 0xc3 : 0xc2;
    mp_buf_append(L,buf,&b,1);
}

/* Lua 5.3 has a built in 64-bit integer type */
void mp_encode_lua_integer(lua_State *L, mp_buf *buf) {
#if (LUA_VERSION_NUM < 503) && BITS_32
    lua_Number i = lua_tonumber(L,-1);
#else
    lua_Integer i = lua_tointeger(L,-1);
#endif
    mp_encode_int(L, buf, (int64_t)i);
}

/* Lua 5.2 and lower only has 64-bit doubles, so we need to
 * detect if the double may be representable as an int
 * for Lua < 5.3 */
void mp_encode_lua_number(lua_State *L, mp_buf *buf) {
    lua_Number n = lua_tonumber(L,-1);

    if (IS_INT64_EQUIVALENT(n)) {
        mp_encode_lua_integer(L, buf);
    } else {
        mp_encode_double(L,buf,(double)n);
    }
}

void mp_encode_lua_type(lua_State *L, mp_buf *buf, int level);

/* Convert a lua table into a message pack list. */
void mp_encode_lua_table_as_array(lua_State *L, mp_buf *buf, int level) {
#if LUA_VERSION_NUM < 502
    size_t len = lua_objlen(L,-1), j;
#else
    size_t len = lua_rawlen(L,-1), j;
#endif

    mp_encode_array(L,buf,len);
    luaL_checkstack(L, 1, "in function mp_encode_lua_table_as_array");
    for (j = 1; j <= len; j++) {
        lua_pushnumber(L,j);
        lua_gettable(L,-2);
        mp_encode_lua_type(L,buf,level+1);
    }
}