MIPS: math-emu: Fix m{add,sub}.s shifts

The code in _sp_maddf (formerly ieee754sp_madd) appears to have been
copied verbatim from ieee754sp_add, and although it's adding the
unpacked "r" & "z" floats it kept using macros that operate on "x" &
"y". This led to the addition being carried out incorrectly on some
mismash of the product, accumulator & multiplicand fields. Typically
this would lead to the assertions "ze == re" & "ze <= SP_EMAX" failing
since ze & re hadn't been operated upon.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: e24c3bec3e8e ("MIPS: math-emu: Add support for the MIPS R6 MADDF FPU instruction")
Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
Cc: Maciej W. Rozycki <macro@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13159/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/ieee754sp.c

@@ -141,7 +141,8 @@ union ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 		} else {
 			/* sticky right shift es bits
 			 */
-			SPXSRSXn(es);
+			xm = XSPSRS(xm, es);
+			xe += es;
 			assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
 			assert(xe == SP_EMIN);
 		}

arch/mips/math-emu/ieee754sp.h

@@ -46,19 +46,17 @@ static inline int ieee754sp_finite(union ieee754sp x)
 }
 
 /* 3bit extended single precision sticky right shift */
-#define SPXSRSXn(rs)							\
-	(xe += rs,							\
-	 xm = (rs > (SP_FBITS+3))?1:((xm) >> (rs)) | ((xm) << (32-(rs)) != 0))
+#define XSPSRS(v, rs)						\
+	((rs > (SP_FBITS+3))?1:((v) >> (rs)) | ((v) << (32-(rs)) != 0))
 
-#define SPXSRSX1() \
-	(xe++, (xm = (xm >> 1) | (xm & 1)))
+#define XSPSRS1(m) \
+	((m >> 1) | (m & 1))
 
-#define SPXSRSYn(rs)								\
-	(ye+=rs,								\
-	 ym = (rs > (SP_FBITS+3))?1:((ym) >> (rs)) | ((ym) << (32-(rs)) != 0))
+#define SPXSRSX1() \
+	(xe++, (xm = XSPSRS1(xm)))
 
 #define SPXSRSY1() \
-	(ye++, (ym = (ym >> 1) | (ym & 1)))
+	(ye++, (ym = XSPSRS1(ym)))
 
 /* convert denormal to normalized with extended exponent */
 #define SPDNORMx(m,e) \

arch/mips/math-emu/sp_add.c

@@ -132,13 +132,15 @@ union ieee754sp ieee754sp_add(union ieee754sp x, union ieee754sp y)
 		 * Have to shift y fraction right to align.
 		 */
 		s = xe - ye;
-		SPXSRSYn(s);
+		ym = XSPSRS(ym, s);
+		ye += s;
 	} else if (ye > xe) {
 		/*
 		 * Have to shift x fraction right to align.
 		 */
 		s = ye - xe;
-		SPXSRSXn(s);
+		xm = XSPSRS(xm, s);
+		xe += s;
 	}
 	assert(xe == ye);
 	assert(xe <= SP_EMAX);

arch/mips/math-emu/sp_maddf.c

@@ -214,16 +214,18 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
 
 	if (ze > re) {
 		/*
-		 * Have to shift y fraction right to align.
+		 * Have to shift r fraction right to align.
 		 */
 		s = ze - re;
-		SPXSRSYn(s);
+		rm = XSPSRS(rm, s);
+		re += s;
 	} else if (re > ze) {
 		/*
-		 * Have to shift x fraction right to align.
+		 * Have to shift z fraction right to align.
 		 */
 		s = re - ze;
-		SPXSRSYn(s);
+		zm = XSPSRS(zm, s);
+		ze += s;
 	}
 	assert(ze == re);
 	assert(ze <= SP_EMAX);
@@ -236,7 +238,8 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
 		zm = zm + rm;
 
 		if (zm >> (SP_FBITS + 1 + 3)) { /* carry out */
-			SPXSRSX1();
+			zm = XSPSRS1(zm);
+			ze++;
 		}
 	} else {
 		if (zm >= rm) {

arch/mips/math-emu/sp_sub.c

@@ -134,13 +134,15 @@ union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y)
 		 * have to shift y fraction right to align
 		 */
 		s = xe - ye;
-		SPXSRSYn(s);
+		ym = XSPSRS(ym, s);
+		ye += s;
 	} else if (ye > xe) {
 		/*
 		 * have to shift x fraction right to align
 		 */
 		s = ye - xe;
-		SPXSRSXn(s);
+		xm = XSPSRS(xm, s);
+		xe += s;
 	}
 	assert(xe == ye);
 	assert(xe <= SP_EMAX);