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Fixed bug in 'string.format' with option '%f'

Browse Source 
As an example, 'print(string.format("%.99f", 1e70))' may have a
lot of garbage after the number.

The old test to ensure that 'string.format("%.99f", n)' was not too
large, 'fabs(n) < 1e100', assumes that the number will fit in the 99
bytes; but the 99 is not the space for the number, it is the added
extra zeros.  The option worked for smaller numbers because of the
extra space added to MAX_ITEM.
This commit is contained in:
Roberto Ierusalimschy 2019-07-23 12:46:33 -03:00
parent 9e6807c3c9
commit 7f5c31cdca
2 changed files with 12 additions and 8 deletions
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14
lstrlib.c
View File

@ -1227,16 +1227,14 @@ static int str_format (lua_State *L) {
nb = lua_number2strx(L, buff, maxitem, form,
luaL_checknumber(L, arg));
break;
case 'e': case 'E': case 'f':
case 'g': case 'G': {
case 'f':
maxitem = MAX_ITEMF; /* extra space for '%f' */
buff = luaL_prepbuffsize(&b, maxitem);
/* FALLTHROUGH */
case 'e': case 'E': case 'g': case 'G': {
lua_Number n = luaL_checknumber(L, arg);
if (*(strfrmt - 1) == 'f' && l_mathop(fabs)(n) >= 1e100) {
/* 'n' needs more than 99 digits */
maxitem = MAX_ITEMF; /* extra space for '%f' */
buff = luaL_prepbuffsize(&b, maxitem);
}
addlenmod(form, LUA_NUMBER_FRMLEN);
nb = l_sprintf(buff, maxitem, form, (LUAI_UACNUMBER)n);
nb = snprintf(buff, maxitem, form, (LUAI_UACNUMBER)n);
break;
}
case 'p': {

6
testes/strings.lua
View File

@ -255,6 +255,12 @@ do -- longest number that can be formatted
local s = string.format('%.99f', -(10^i))
assert(string.len(s) >= i + 101)
assert(tonumber(s) == -(10^i))
-- limit for floats
assert(10^38 < math.huge)
local s = string.format('%.99f', -(10^38))
assert(string.len(s) >= 38 + 101)
assert(tonumber(s) == -(10^38))
end