MIPS: math-emu: Handle zero accumulator case in MADDF and MSUBF separately

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@imgtec.com>
Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
Cc: James.Hogan@imgtec.com
Cc: Paul.Burton@imgtec.com
Cc: Raghu.Gandham@imgtec.com
Cc: Leonid.Yegoshin@imgtec.com
Cc: Douglas.Leung@imgtec.com
Cc: Petar.Jovanovic@imgtec.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16512/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/dp_maddf.c

@@ -54,7 +54,7 @@ static union ieee754dp _dp_maddf(union ieee754dp z, union ieee754dp x,
 		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 ieee754dp z, union ieee754dp x,
 	}
 	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);
 

arch/mips/math-emu/sp_maddf.c

@@ -54,7 +54,7 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
 		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 ieee754sp z, union ieee754sp x,
 	}
 	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);