linux-kernel - [PATCH 4.9 19/77] MIPS: math-emu: Handle zero accumulator case in MADDF and MSUBF separately

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Message-Id: <20170924203243.631443417@linuxfoundation.org>
Date:   Sun, 24 Sep 2017 22:32:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miodrag Dinic <miodrag.dinic@...tec.com>,
        Goran Ferenc <goran.ferenc@...tec.com>,
        Aleksandar Markovic <aleksandar.markovic@...tec.com>,
        James.Hogan@...tec.com, Paul.Burton@...tec.com,
        Raghu.Gandham@...tec.com, Leonid.Yegoshin@...tec.com,
        Douglas.Leung@...tec.com, Petar.Jovanovic@...tec.com,
        linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>
Subject: [PATCH 4.9 19/77] MIPS: math-emu: Handle zero accumulator case in MADDF and MSUBF separately

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aleksandar Markovic <aleksandar.markovic@...tec.com>

commit ddbfff7429a75d954bf5bdff9f2222bceb4c236a upstream.

If accumulator value is zero, just return the value of previously
calculated product. This brings logic in MADDF/MSUBF implementation
closer to the logic in ADD/SUB case.

Signed-off-by: Miodrag Dinic <miodrag.dinic@...tec.com>
Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>
Cc: James.Hogan@...tec.com
Cc: Paul.Burton@...tec.com
Cc: Raghu.Gandham@...tec.com
Cc: Leonid.Yegoshin@...tec.com
Cc: Douglas.Leung@...tec.com
Cc: Petar.Jovanovic@...tec.com
Cc: linux-mips@...ux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16512/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/math-emu/dp_maddf.c |    5 ++++-
 arch/mips/math-emu/sp_maddf.c |    5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/arch/mips/math-emu/dp_maddf.c
+++ b/arch/mips/math-emu/dp_maddf.c
@@ -54,7 +54,7 @@ static union ieee754dp _dp_maddf(union i
 		return ieee754dp_nanxcpt(z);
 	case IEEE754_CLASS_DNORM:
 		DPDNORMZ;
-	/* QNAN is handled separately below */
+	/* QNAN and ZERO cases are handled separately below */
 	}
 
 	switch (CLPAIR(xc, yc)) {
@@ -210,6 +210,9 @@ static union ieee754dp _dp_maddf(union i
 	}
 	assert(rm & (DP_HIDDEN_BIT << 3));
 
+	if (zc == IEEE754_CLASS_ZERO)
+		return ieee754dp_format(rs, re, rm);
+
 	/* And now the addition */
 	assert(zm & DP_HIDDEN_BIT);
 
--- a/arch/mips/math-emu/sp_maddf.c
+++ b/arch/mips/math-emu/sp_maddf.c
@@ -54,7 +54,7 @@ static union ieee754sp _sp_maddf(union i
 		return ieee754sp_nanxcpt(z);
 	case IEEE754_CLASS_DNORM:
 		SPDNORMZ;
-	/* QNAN is handled separately below */
+	/* QNAN and ZERO cases are handled separately below */
 	}
 
 	switch (CLPAIR(xc, yc)) {
@@ -203,6 +203,9 @@ static union ieee754sp _sp_maddf(union i
 	}
 	assert(rm & (SP_HIDDEN_BIT << 3));
 
+	if (zc == IEEE754_CLASS_ZERO)
+		return ieee754sp_format(rs, re, rm);
+
 	/* And now the addition */
 
 	assert(zm & SP_HIDDEN_BIT);