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Fix a bug that exponent overflow is ignored in add, sub, mult and div operation #367

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Merged
tompng merged 2 commits into from
Jul 10, 2025
Merged

Fix a bug that exponent overflow is ignored in add, sub, mult and div operation #367

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1ee52bb
Fix a bug that exponent overflow is ignored in x+y and x-y
tompng Jul 10, 2025
7902239
Fix div and mult sign when result overflows or underflows
tompng Jul 10, 2025
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23 changes: 12 additions & 11 deletions ext/bigdecimal/bigdecimal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5489,7 +5489,7 @@ VpAsgn(Real *c, Real *a, int isw)
VP_EXPORT size_t
VpAddSub(Real *c, Real *a, Real *b, int operation)
{
short sw, isw;
short sw, isw, sign;
Real *a_ptr, *b_ptr;
size_t n, na, nb, i;
DECDIG mrv;
Expand Down Expand Up @@ -5590,19 +5590,20 @@ VpAddSub(Real *c, Real *a, Real *b, int operation)
if (isw) { /* addition */
VpSetSign(c, 1);
mrv = VpAddAbs(a_ptr, b_ptr, c);
VpSetSign(c, isw / 2);
sign = isw / 2;
}
else { /* subtraction */
VpSetSign(c, 1);
mrv = VpSubAbs(a_ptr, b_ptr, c);
if (a_ptr == a) {
VpSetSign(c,VpGetSign(a));
}
else {
VpSetSign(c, VpGetSign(a_ptr) * sw);
}
sign = a_ptr == a ? VpGetSign(a) : VpGetSign(a_ptr) * sw;
}
if (VpIsInf(c)) {
VpSetInf(c, sign);
}
else {
VpSetSign(c, sign);
VpInternalRound(c, 0, (c->Prec > 0) ? c->frac[c->Prec-1] : 0, mrv);
}
VpInternalRound(c, 0, (c->Prec > 0) ? c->frac[c->Prec-1] : 0, mrv);

#ifdef BIGDECIMAL_DEBUG
if (gfDebug) {
Expand Down Expand Up @@ -5995,11 +5996,11 @@ VpMult(Real *c, Real *a, Real *b)
/* set LHSV c info */

c->exponent = a->exponent; /* set exponent */
VpSetSign(c, VpGetSign(a) * VpGetSign(b)); /* set sign */
if (!AddExponent(c, b->exponent)) {
if (w) rbd_free_struct(c);
return 0;
}
VpSetSign(c, VpGetSign(a) * VpGetSign(b)); /* set sign */
carry = 0;
nc = ind_c = MxIndAB;
memset(c->frac, 0, (nc + 1) * sizeof(DECDIG)); /* Initialize c */
Expand Down Expand Up @@ -6246,10 +6247,10 @@ VpDivd(Real *c, Real *r, Real *a, Real *b)
out_side:
c->Prec = word_c;
c->exponent = a->exponent;
VpSetSign(c, VpGetSign(a) * VpGetSign(b));
if (!AddExponent(c, 2)) return 0;
if (!AddExponent(c, -(b->exponent))) return 0;

VpSetSign(c, VpGetSign(a) * VpGetSign(b));
VpNmlz(c); /* normalize c */
r->Prec = word_r;
r->exponent = a->exponent;
Expand Down
39 changes: 39 additions & 0 deletions test/bigdecimal/test_bigdecimal.rb
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Expand Up @@ -460,6 +460,45 @@ def test_exception_overflow
end
end

def test_mult_div_overflow_underflow_sign
BigDecimal.mode(BigDecimal::EXCEPTION_OVERFLOW, false)
BigDecimal.mode(BigDecimal::EXCEPTION_UNDERFLOW, false)

large_x = BigDecimal("10")
100.times do
x2 = large_x * large_x
break if x2.infinite?
large_x = x2
end

small_x = BigDecimal("0.1")
100.times do
x2 = small_x * small_x
break if x2.zero?
small_x = x2
end

assert_positive_infinite(large_x * large_x)
assert_negative_infinite(large_x * (-large_x))
assert_negative_infinite((-large_x) * large_x)
assert_positive_infinite((-large_x) * (-large_x))

assert_positive_zero(small_x * small_x)
assert_negative_zero(small_x * (-small_x))
assert_negative_zero((-small_x) * small_x)
assert_positive_zero((-small_x) * (-small_x))

assert_positive_infinite(large_x.div(small_x, 10))
assert_negative_infinite(large_x.div(-small_x, 10))
assert_negative_infinite((-large_x).div(small_x, 10))
assert_positive_infinite((-large_x).div(-small_x, 10))

assert_positive_zero(small_x.div(large_x, 10))
assert_negative_zero(small_x.div(-large_x, 10))
assert_negative_zero((-small_x).div(large_x, 10))
assert_positive_zero((-small_x).div(-large_x, 10))
end

def test_exception_zerodivide
BigDecimal.mode(BigDecimal::EXCEPTION_OVERFLOW, false)
_test_mode(BigDecimal::EXCEPTION_ZERODIVIDE) { 1 / BigDecimal("0") }
Expand Down