From 2830b0b8655f0d1a62b416af8ade31f5b96f0ffb Mon Sep 17 00:00:00 2001
From: Georg-Johann Lay <avr@gjlay.de>
Date: Fri, 14 Jun 2024 18:24:13 +0200
Subject: [PATCH] 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.
---
libgcc/config/avr/libf7/libf7.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/libgcc/config/avr/libf7/libf7.c b/libgcc/config/avr/libf7/libf7.c
index 375becb854c1..6fae4fc1a2de 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;
--
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