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author | Georg-Johann Lay <avr@gjlay.de> | 2024-06-14 18:24:13 +0200 |
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committer | Georg-Johann Lay <avr@gjlay.de> | 2024-06-14 18:33:05 +0200 |
commit | 2830b0b8655f0d1a62b416af8ade31f5b96f0ffb (patch) | |
tree | 58c4ad76c2e285c4fedd094c7ea32b83b495d370 /libgcc/config/avr | |
parent | 6af8d8e618ed27dae3432c96484de4360bd893ab (diff) | |
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AVR: target/115419 - Tie breaks are rounded-to-even.
libgcc/config/avr/libf7/
PR target/115419
* libf7.c (f7_get_double): Round tie breaks to even LSB.
Diffstat (limited to 'libgcc/config/avr')
-rw-r--r-- | libgcc/config/avr/libf7/libf7.c | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/libgcc/config/avr/libf7/libf7.c b/libgcc/config/avr/libf7/libf7.c index 375becb..6fae4fc 100644 --- a/libgcc/config/avr/libf7/libf7.c +++ b/libgcc/config/avr/libf7/libf7.c @@ -440,11 +440,21 @@ f7_double_t f7_get_double (const f7_t *aa) mant &= 0x00ffffffffffffff; - // FIXME: For subnormals, rounding is premature and should be - // done *after* the mantissa has been shifted into place - // (or the round value be shifted left accordingly). - // Round. - mant += 1u << (F7_MANT_BITS - (1 + DBL_DIG_MANT) - 1); + // PR115419: The least significant nibble tells how to round: + // Tie breaks are rounded to even (Banker's rounding). + uint8_t lsn = mant & 0xff; + lsn &= 0xf; + // The LSB of the outgoing double is at bit 3. + if (lsn & (1 << 3)) + ++lsn; + if (lsn > (1 << 2)) + { + // FIXME: For subnormals, rounding is premature and should be + // done *after* the mantissa has been shifted into place + // (or the round value be shifted left accordingly). + // Round. + mant += 1u << (F7_MANT_BITS - (1 + DBL_DIG_MANT) - 1); + } uint8_t dex; register uint64_t r18 __asm ("r18") = mant; |