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Commit db57f29d authored by Paul Burton's avatar Paul Burton Committed by Ralf Baechle
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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: default avatarPaul Burton <paul.burton@imgtec.com>
Fixes: e24c3bec ("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: default avatarRalf Baechle <ralf@linux-mips.org>
parent 5c18c936

arch/mips/math-emu/ieee754sp.c

+2 −1
Original line number Diff line number Diff line
@@ -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

+7 −9
Original line number Diff line number Diff line
@@ -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

+4 −2
Original line number Diff line number Diff line
@@ -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

+8 −5
Original line number Diff line number Diff line
@@ -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

+4 −2
Original line number Diff line number Diff line
@@ -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);