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commit 7f5c31cdcac5388b3c48a26112dfb6d2cadb7321
parent 9e6807c3c9d5036e999f636f936df07b72284442
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date:   Tue, 23 Jul 2019 12:46:06 -0300

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

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.

Diffstat:
Mlstrlib.c | 14++++++--------
Mtestes/strings.lua | 6++++++
2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/lstrlib.c b/lstrlib.c @@ -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': { diff --git a/testes/strings.lua b/testes/strings.lua @@ -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