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Fix (rare) problem of exponent overflow when rounding.

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This commit is contained in:
Olaf Seibert 2021-01-21 20:06:53 +01:00
parent c559f1b65f
commit 8193f2c2cd
1 changed files with 17 additions and 3 deletions
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20
parse.c
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@ -474,6 +474,8 @@ int parse_float(
* Exponent (8 bits)
* Mantissa (7 bits)
*/
uint64_t unrounded_ufrac = ufrac;
if (size < 4) {
/*
* Round to nearest 8- or 24- bit approximation.
@ -502,9 +504,21 @@ int parse_float(
}
if ((ufrac >> 56) > 0) { /* Overflow? */
ufrac >>= 1; /* Normalize */
uexp++;
DF(("ufrac: %016lx uexp: %02x\n", ufrac, uexp));
if (uexp < 0xFF) {
ufrac >>= 1; /* Normalize */
uexp++;
DF(("ufrac: %016lx uexp: %02x\n", ufrac, uexp));
} else {
/*
* If rounding and then normalisation would cause the exponent to
* overflow, just don't round: the cure is worse than the disease.
* We could detect ahead of time but the conditions for all size
* values may be a bit complicated, and so rare, that it is more
* readable to just undo it here.
*/
ufrac = unrounded_ufrac;
DF(("don't round: exponent overflow", ufrac, uexp));
}
}
flt[0] = (unsigned) (sign | (uexp << 7) | ((ufrac >> 48) & 0x7F));