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Refactor AddExponent overflow/underflow check #368

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Merged
tompng merged 1 commit into from
Jul 11, 2025
Merged

Refactor AddExponent overflow/underflow check #368

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31 changes: 13 additions & 18 deletions ext/bigdecimal/bigdecimal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,11 @@
#define SIGNED_VALUE_MIN INTPTR_MIN
#define MUL_OVERFLOW_SIGNED_VALUE_P(a, b) MUL_OVERFLOW_SIGNED_INTEGER_P(a, b, SIGNED_VALUE_MIN, SIGNED_VALUE_MAX)

/* max_value = 0.9999_9999_9999E[exponent], exponent <= SIGNED_VALUE_MAX */
#define VP_EXPONENT_MAX (SIGNED_VALUE_MAX / BASE_FIG)
/* min_value = 0.0001_0000_0000E[exponent], exponent-(BASE_FIG-1) >= SIGNED_VALUE_MIN */
#define VP_EXPONENT_MIN ((SIGNED_VALUE_MIN + BASE_FIG - 1) / BASE_FIG)

VALUE rb_cBigDecimal;
VALUE rb_mBigMath;

Expand Down Expand Up @@ -5084,24 +5089,14 @@ AddExponent(Real *a, SIGNED_VALUE n)
{
SIGNED_VALUE e = a->exponent;
SIGNED_VALUE m = e+n;
SIGNED_VALUE eb, mb;
if (e > 0) {
if (n > 0) {
if (MUL_OVERFLOW_SIGNED_VALUE_P(m, (SIGNED_VALUE)BASE_FIG) ||
MUL_OVERFLOW_SIGNED_VALUE_P(e, (SIGNED_VALUE)BASE_FIG))
goto overflow;
mb = m*(SIGNED_VALUE)BASE_FIG;
eb = e*(SIGNED_VALUE)BASE_FIG;
if (eb - mb > 0) goto overflow;
}
}
else if (n < 0) {
if (MUL_OVERFLOW_SIGNED_VALUE_P(m, (SIGNED_VALUE)BASE_FIG) ||
MUL_OVERFLOW_SIGNED_VALUE_P(e, (SIGNED_VALUE)BASE_FIG))
goto underflow;
mb = m*(SIGNED_VALUE)BASE_FIG;
eb = e*(SIGNED_VALUE)BASE_FIG;
if (mb - eb > 0) goto underflow;
if (e > 0 && n > 0) {
if (n > VP_EXPONENT_MAX - e) goto overflow;
} else if (e < 0 && n < 0) {
if (n < VP_EXPONENT_MIN - e) goto underflow;
} else if (m > VP_EXPONENT_MAX) {
goto overflow;
} else if (m < VP_EXPONENT_MIN) {
goto underflow;
}
a->exponent = m;
return 1;
Expand Down