Function luaV_concat

Source/Misc/lua/src/lua.c:15111–15143

void luaV_concat (lua_State *L, int total, int last) {
do {
StkId top = L->base + last + 1;
int n = 2;  /* number of elements handled in this pass (at least 2) */
if (!(ttisstring(top-2) || ttisnumber(top-2)) || !tostring(L, top-1)) {
if (!call_binTM(L, top-2, top-1, top-2, TM_CONCAT))
luaG_concaterror(L, top-2, top-1);
} else if (tsvalue(top-1)->len == 0)  /* second op is empty? */
(void)tostring(L, top - 2);  /* result is first op (as string) */
else {
/* at least two string values; get as many as possible */
size_t tl = tsvalue(top-1)->len;
char *buffer;
int i;
/* collect total length */
for (n = 1; n < total && tostring(L, top-n-1); n++) {
size_t l = tsvalue(top-n-1)->len;
if (l >= MAX_SIZET - tl) luaG_runerror(L, "string length overflow");
tl += l;
}
buffer = luaZ_openspace(L, &G(L)->buff, tl);
tl = 0;
for (i=n; i>0; i--) {  /* concat all strings */
size_t l = tsvalue(top-i)->len;
memcpy(buffer+tl, svalue(top-i), l);
tl += l;
}
setsvalue2s(L, top-n, luaS_newlstr(L, buffer, tl));
}
total -= n-1;  /* got `n' strings to create 1 new */
last -= n-1;
} while (total > 1);  /* repeat until only 1 result left */
}


static void Arith (lua_State *L, StkId ra, const TValue *rb,