MIPS: math-emu: Add IEEE Std 754-2008 NaN encoding emulation

Implement IEEE Std 754-2008 NaN encoding wired to the state of the
FCSR.NAN2008 bit.  Make the interpretation of the quiet bit in NaN data
as follows:

* in the legacy mode originally defined by the MIPS architecture the
  value of 1 denotes an sNaN whereas the value of 0 denotes a qNaN,

* in the 2008 mode introduced with revision 5 of the MIPS architecture
  the value of 0 denotes an sNaN whereas the value of 1 denotes a qNaN,
  following the definition of the preferred NaN encoding introduced with
  IEEE Std 754-2008.

In the 2008 mode, following the requirement of the said standard, quiet
an sNaN where needed by setting the quiet bit to 1 and leaving all the
NaN payload bits unchanged.

Update format conversion operations according to the rules set by IEEE
Std 754-2008 and the MIPS architecture.  Specifically:

* propagate NaN payload bits through conversions between floating-point
  formats such that as much information as possible is preserved and
  specifically a conversion from a narrower format to a wider format and
  then back to the original format does not change a qNaN payload in any
  way,

* conversions from a floating-point to an integer format where the
  source is a NaN, infinity or a value that would convert to an integer
  outside the range of the result format produce, under the default
  exception handling, the respective values defined by the MIPS
  architecture.

In full FPU emulation set the FIR.HAS2008 bit to 1, however do not make
any further FCSR bits writable.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Fortune <Matthew.Fortune@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11477/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 758b625..937e653 100644 (file)
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -113,6 +113,8 @@ static void cpu_set_nofpu_id(struct cpuinfo_mips *c)
        if (c->isa_level & (MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
                            MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6))
                value |= MIPS_FPIR_F64 | MIPS_FPIR_L | MIPS_FPIR_W;
+       if (c->options & MIPS_CPU_NAN_2008)
+               value |= MIPS_FPIR_HAS2008;
        c->fpu_id = value;
 }
 

diff --git a/arch/mips/math-emu/dp_tint.c b/arch/mips/math-emu/dp_tint.c
index 6ffc336..f398561 100644 (file)
--- a/arch/mips/math-emu/dp_tint.c
+++ b/arch/mips/math-emu/dp_tint.c
@@ -38,10 +38,13 @@ int ieee754dp_tint(union ieee754dp x)
        switch (xc) {
        case IEEE754_CLASS_SNAN:
        case IEEE754_CLASS_QNAN:
-       case IEEE754_CLASS_INF:
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754si_indef();
 
+       case IEEE754_CLASS_INF:
+               ieee754_setcx(IEEE754_INVALID_OPERATION);
+               return ieee754si_overflow(xs);
+
        case IEEE754_CLASS_ZERO:
                return 0;
 
@@ -53,7 +56,7 @@ int ieee754dp_tint(union ieee754dp x)
                /* Set invalid. We will only use overflow for floating
                   point overflow */
                ieee754_setcx(IEEE754_INVALID_OPERATION);
-               return ieee754si_indef();
+               return ieee754si_overflow(xs);
        }
        /* oh gawd */
        if (xe > DP_FBITS) {
@@ -93,7 +96,7 @@ int ieee754dp_tint(union ieee754dp x)
                if ((xm >> 31) != 0 && (xs == 0 || xm != 0x80000000)) {
                        /* This can happen after rounding */
                        ieee754_setcx(IEEE754_INVALID_OPERATION);
-                       return ieee754si_indef();
+                       return ieee754si_overflow(xs);
                }
                if (round || sticky)
                        ieee754_setcx(IEEE754_INEXACT);

diff --git a/arch/mips/math-emu/dp_tlong.c b/arch/mips/math-emu/dp_tlong.c
index 9cdc145..748fa10 100644 (file)
--- a/arch/mips/math-emu/dp_tlong.c
+++ b/arch/mips/math-emu/dp_tlong.c
@@ -38,10 +38,13 @@ s64 ieee754dp_tlong(union ieee754dp x)
        switch (xc) {
        case IEEE754_CLASS_SNAN:
        case IEEE754_CLASS_QNAN:
-       case IEEE754_CLASS_INF:
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754di_indef();
 
+       case IEEE754_CLASS_INF:
+               ieee754_setcx(IEEE754_INVALID_OPERATION);
+               return ieee754di_overflow(xs);
+
        case IEEE754_CLASS_ZERO:
                return 0;
 
@@ -56,7 +59,7 @@ s64 ieee754dp_tlong(union ieee754dp x)
                /* Set invalid. We will only use overflow for floating
                   point overflow */
                ieee754_setcx(IEEE754_INVALID_OPERATION);
-               return ieee754di_indef();
+               return ieee754di_overflow(xs);
        }
        /* oh gawd */
        if (xe > DP_FBITS) {
@@ -97,7 +100,7 @@ s64 ieee754dp_tlong(union ieee754dp x)
                if ((xm >> 63) != 0) {
                        /* This can happen after rounding */
                        ieee754_setcx(IEEE754_INVALID_OPERATION);
-                       return ieee754di_indef();
+                       return ieee754di_overflow(xs);
                }
                if (round || sticky)
                        ieee754_setcx(IEEE754_INEXACT);

diff --git a/arch/mips/math-emu/ieee754.c b/arch/mips/math-emu/ieee754.c
index 8e97acb..e16ae7b 100644 (file)
--- a/arch/mips/math-emu/ieee754.c
+++ b/arch/mips/math-emu/ieee754.c
@@ -59,7 +59,8 @@ const union ieee754dp __ieee754dp_spcvals[] = {
        DPCNST(1, 3,           0x4000000000000ULL),     /* - 10.0   */
        DPCNST(0, DP_EMAX + 1, 0x0000000000000ULL),     /* + infinity */
        DPCNST(1, DP_EMAX + 1, 0x0000000000000ULL),     /* - infinity */
-       DPCNST(0, DP_EMAX + 1, 0x7FFFFFFFFFFFFULL),     /* + indef quiet Nan */
+       DPCNST(0, DP_EMAX + 1, 0x7FFFFFFFFFFFFULL),     /* + ind legacy qNaN */
+       DPCNST(0, DP_EMAX + 1, 0x8000000000000ULL),     /* + indef 2008 qNaN */
        DPCNST(0, DP_EMAX,     0xFFFFFFFFFFFFFULL),     /* + max */
        DPCNST(1, DP_EMAX,     0xFFFFFFFFFFFFFULL),     /* - max */
        DPCNST(0, DP_EMIN,     0x0000000000000ULL),     /* + min normal */
@@ -82,7 +83,8 @@ const union ieee754sp __ieee754sp_spcvals[] = {
        SPCNST(1, 3,           0x200000),       /* - 10.0   */
        SPCNST(0, SP_EMAX + 1, 0x000000),       /* + infinity */
        SPCNST(1, SP_EMAX + 1, 0x000000),       /* - infinity */
-       SPCNST(0, SP_EMAX + 1, 0x3FFFFF),       /* + indef quiet Nan  */
+       SPCNST(0, SP_EMAX + 1, 0x3FFFFF),       /* + indef legacy quiet NaN */
+       SPCNST(0, SP_EMAX + 1, 0x400000),       /* + indef 2008 quiet NaN */
        SPCNST(0, SP_EMAX,     0x7FFFFF),       /* + max normal */
        SPCNST(1, SP_EMAX,     0x7FFFFF),       /* - max normal */
        SPCNST(0, SP_EMIN,     0x000000),       /* + min normal */

diff --git a/arch/mips/math-emu/ieee754.h b/arch/mips/math-emu/ieee754.h
index df94720..d3be351 100644 (file)
--- a/arch/mips/math-emu/ieee754.h
+++ b/arch/mips/math-emu/ieee754.h
@@ -221,15 +221,16 @@ union ieee754dp ieee754dp_dump(char *s, union ieee754dp x);
 #define IEEE754_SPCVAL_NTEN            5       /* -10.0 */
 #define IEEE754_SPCVAL_PINFINITY       6       /* +inf */
 #define IEEE754_SPCVAL_NINFINITY       7       /* -inf */
-#define IEEE754_SPCVAL_INDEF           8       /* quiet NaN */
-#define IEEE754_SPCVAL_PMAX            9       /* +max norm */
-#define IEEE754_SPCVAL_NMAX            10      /* -max norm */
-#define IEEE754_SPCVAL_PMIN            11      /* +min norm */
-#define IEEE754_SPCVAL_NMIN            12      /* -min norm */
-#define IEEE754_SPCVAL_PMIND           13      /* +min denorm */
-#define IEEE754_SPCVAL_NMIND           14      /* -min denorm */
-#define IEEE754_SPCVAL_P1E31           15      /* + 1.0e31 */
-#define IEEE754_SPCVAL_P1E63           16      /* + 1.0e63 */
+#define IEEE754_SPCVAL_INDEF_LEG       8       /* legacy quiet NaN */
+#define IEEE754_SPCVAL_INDEF_2008      9       /* IEEE 754-2008 quiet NaN */
+#define IEEE754_SPCVAL_PMAX            10      /* +max norm */
+#define IEEE754_SPCVAL_NMAX            11      /* -max norm */
+#define IEEE754_SPCVAL_PMIN            12      /* +min norm */
+#define IEEE754_SPCVAL_NMIN            13      /* -min norm */
+#define IEEE754_SPCVAL_PMIND           14      /* +min denorm */
+#define IEEE754_SPCVAL_NMIND           15      /* -min denorm */
+#define IEEE754_SPCVAL_P1E31           16      /* + 1.0e31 */
+#define IEEE754_SPCVAL_P1E63           17      /* + 1.0e63 */
 
 extern const union ieee754dp __ieee754dp_spcvals[];
 extern const union ieee754sp __ieee754sp_spcvals[];
@@ -243,7 +244,8 @@ extern const union ieee754sp __ieee754sp_spcvals[];
 #define ieee754dp_zero(sn)     (ieee754dp_spcvals[IEEE754_SPCVAL_PZERO+(sn)])
 #define ieee754dp_one(sn)      (ieee754dp_spcvals[IEEE754_SPCVAL_PONE+(sn)])
 #define ieee754dp_ten(sn)      (ieee754dp_spcvals[IEEE754_SPCVAL_PTEN+(sn)])
-#define ieee754dp_indef()      (ieee754dp_spcvals[IEEE754_SPCVAL_INDEF])
+#define ieee754dp_indef()      (ieee754dp_spcvals[IEEE754_SPCVAL_INDEF_LEG + \
+                                                  ieee754_csr.nan2008])
 #define ieee754dp_max(sn)      (ieee754dp_spcvals[IEEE754_SPCVAL_PMAX+(sn)])
 #define ieee754dp_min(sn)      (ieee754dp_spcvals[IEEE754_SPCVAL_PMIN+(sn)])
 #define ieee754dp_mind(sn)     (ieee754dp_spcvals[IEEE754_SPCVAL_PMIND+(sn)])
@@ -254,7 +256,8 @@ extern const union ieee754sp __ieee754sp_spcvals[];
 #define ieee754sp_zero(sn)     (ieee754sp_spcvals[IEEE754_SPCVAL_PZERO+(sn)])
 #define ieee754sp_one(sn)      (ieee754sp_spcvals[IEEE754_SPCVAL_PONE+(sn)])
 #define ieee754sp_ten(sn)      (ieee754sp_spcvals[IEEE754_SPCVAL_PTEN+(sn)])
-#define ieee754sp_indef()      (ieee754sp_spcvals[IEEE754_SPCVAL_INDEF])
+#define ieee754sp_indef()      (ieee754sp_spcvals[IEEE754_SPCVAL_INDEF_LEG + \
+                                                  ieee754_csr.nan2008])
 #define ieee754sp_max(sn)      (ieee754sp_spcvals[IEEE754_SPCVAL_PMAX+(sn)])
 #define ieee754sp_min(sn)      (ieee754sp_spcvals[IEEE754_SPCVAL_PMIN+(sn)])
 #define ieee754sp_mind(sn)     (ieee754sp_spcvals[IEEE754_SPCVAL_PMIND+(sn)])
@@ -266,12 +269,25 @@ extern const union ieee754sp __ieee754sp_spcvals[];
  */
 static inline int ieee754si_indef(void)
 {
-       return INT_MAX;
+       return ieee754_csr.nan2008 ? 0 : INT_MAX;
 }
 
 static inline s64 ieee754di_indef(void)
 {
-       return S64_MAX;
+       return ieee754_csr.nan2008 ? 0 : S64_MAX;
+}
+
+/*
+ * Overflow integer value
+ */
+static inline int ieee754si_overflow(int xs)
+{
+       return ieee754_csr.nan2008 && xs ? INT_MIN : INT_MAX;
+}
+
+static inline s64 ieee754di_overflow(int xs)
+{
+       return ieee754_csr.nan2008 && xs ? S64_MIN : S64_MAX;
 }
 
 /* result types for xctx.rt */

diff --git a/arch/mips/math-emu/ieee754dp.c b/arch/mips/math-emu/ieee754dp.c
index 522d843..ad3c734 100644 (file)
--- a/arch/mips/math-emu/ieee754dp.c
+++ b/arch/mips/math-emu/ieee754dp.c
@@ -37,8 +37,11 @@ static inline int ieee754dp_isnan(union ieee754dp x)
 
 static inline int ieee754dp_issnan(union ieee754dp x)
 {
+       int qbit;
+
        assert(ieee754dp_isnan(x));
-       return (DPMANT(x) & DP_MBIT(DP_FBITS - 1)) == DP_MBIT(DP_FBITS - 1);
+       qbit = (DPMANT(x) & DP_MBIT(DP_FBITS - 1)) == DP_MBIT(DP_FBITS - 1);
+       return ieee754_csr.nan2008 ^ qbit;
 }
 
 
@@ -51,7 +54,12 @@ union ieee754dp __cold ieee754dp_nanxcpt(union ieee754dp r)
        assert(ieee754dp_issnan(r));
 
        ieee754_setcx(IEEE754_INVALID_OPERATION);
-       return ieee754dp_indef();
+       if (ieee754_csr.nan2008)
+               DPMANT(r) |= DP_MBIT(DP_FBITS - 1);
+       else
+               r = ieee754dp_indef();
+
+       return r;
 }
 
 static u64 ieee754dp_get_rounding(int sn, u64 xm)

diff --git a/arch/mips/math-emu/ieee754int.h b/arch/mips/math-emu/ieee754int.h
index 6383e2c..ed7bb27 100644 (file)
--- a/arch/mips/math-emu/ieee754int.h
+++ b/arch/mips/math-emu/ieee754int.h
@@ -63,10 +63,10 @@ static inline int ieee754_class_nan(int xc)
        if (ve == SP_EMAX+1+SP_EBIAS) {                                 \
                if (vm == 0)                                            \
                        vc = IEEE754_CLASS_INF;                         \
-               else if (vm & SP_MBIT(SP_FBITS-1))                      \
-                       vc = IEEE754_CLASS_SNAN;                        \
-               else                                                    \
+               else if (ieee754_csr.nan2008 ^ !(vm & SP_MBIT(SP_FBITS - 1))) \
                        vc = IEEE754_CLASS_QNAN;                        \
+               else                                                    \
+                       vc = IEEE754_CLASS_SNAN;                        \
        } else if (ve == SP_EMIN-1+SP_EBIAS) {                          \
                if (vm) {                                               \
                        ve = SP_EMIN;                                   \
@@ -97,10 +97,10 @@ static inline int ieee754_class_nan(int xc)
        if (ve == DP_EMAX+1+DP_EBIAS) {                                 \
                if (vm == 0)                                            \
                        vc = IEEE754_CLASS_INF;                         \
-               else if (vm & DP_MBIT(DP_FBITS-1))                      \
-                       vc = IEEE754_CLASS_SNAN;                        \
-               else                                                    \
+               else if (ieee754_csr.nan2008 ^ !(vm & DP_MBIT(DP_FBITS - 1))) \
                        vc = IEEE754_CLASS_QNAN;                        \
+               else                                                    \
+                       vc = IEEE754_CLASS_SNAN;                        \
        } else if (ve == DP_EMIN-1+DP_EBIAS) {                          \
                if (vm) {                                               \
                        ve = DP_EMIN;                                   \

diff --git a/arch/mips/math-emu/ieee754sp.c b/arch/mips/math-emu/ieee754sp.c
index ca8e35e..def00ff 100644 (file)
--- a/arch/mips/math-emu/ieee754sp.c
+++ b/arch/mips/math-emu/ieee754sp.c
@@ -37,8 +37,11 @@ static inline int ieee754sp_isnan(union ieee754sp x)
 
 static inline int ieee754sp_issnan(union ieee754sp x)
 {
+       int qbit;
+
        assert(ieee754sp_isnan(x));
-       return SPMANT(x) & SP_MBIT(SP_FBITS - 1);
+       qbit = (SPMANT(x) & SP_MBIT(SP_FBITS - 1)) == SP_MBIT(SP_FBITS - 1);
+       return ieee754_csr.nan2008 ^ qbit;
 }
 
 
@@ -51,7 +54,12 @@ union ieee754sp __cold ieee754sp_nanxcpt(union ieee754sp r)
        assert(ieee754sp_issnan(r));
 
        ieee754_setcx(IEEE754_INVALID_OPERATION);
-       return ieee754sp_indef();
+       if (ieee754_csr.nan2008)
+               SPMANT(r) |= SP_MBIT(SP_FBITS - 1);
+       else
+               r = ieee754sp_indef();
+
+       return r;
 }
 
 static unsigned ieee754sp_get_rounding(int sn, unsigned xm)

diff --git a/arch/mips/math-emu/sp_fdp.c b/arch/mips/math-emu/sp_fdp.c
index 3797148..5060e8f 100644 (file)
--- a/arch/mips/math-emu/sp_fdp.c
+++ b/arch/mips/math-emu/sp_fdp.c
@@ -44,13 +44,16 @@ union ieee754sp ieee754sp_fdp(union ieee754dp x)
 
        switch (xc) {
        case IEEE754_CLASS_SNAN:
-               return ieee754sp_nanxcpt(ieee754sp_nan_fdp(xs, xm));
-
+               x = ieee754dp_nanxcpt(x);
+               EXPLODEXDP;
+               /* Fall through.  */
        case IEEE754_CLASS_QNAN:
                y = ieee754sp_nan_fdp(xs, xm);
-               EXPLODEYSP;
-               if (!ieee754_class_nan(yc))
-                       y = ieee754sp_indef();
+               if (!ieee754_csr.nan2008) {
+                       EXPLODEYSP;
+                       if (!ieee754_class_nan(yc))
+                               y = ieee754sp_indef();
+               }
                return y;
 
        case IEEE754_CLASS_INF:

diff --git a/arch/mips/math-emu/sp_tint.c b/arch/mips/math-emu/sp_tint.c
index 091299a..f4b4cab 100644 (file)
--- a/arch/mips/math-emu/sp_tint.c
+++ b/arch/mips/math-emu/sp_tint.c
@@ -38,10 +38,13 @@ int ieee754sp_tint(union ieee754sp x)
        switch (xc) {
        case IEEE754_CLASS_SNAN:
        case IEEE754_CLASS_QNAN:
-       case IEEE754_CLASS_INF:
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754si_indef();
 
+       case IEEE754_CLASS_INF:
+               ieee754_setcx(IEEE754_INVALID_OPERATION);
+               return ieee754si_overflow(xs);
+
        case IEEE754_CLASS_ZERO:
                return 0;
 
@@ -56,7 +59,7 @@ int ieee754sp_tint(union ieee754sp x)
                /* Set invalid. We will only use overflow for floating
                   point overflow */
                ieee754_setcx(IEEE754_INVALID_OPERATION);
-               return ieee754si_indef();
+               return ieee754si_overflow(xs);
        }
        /* oh gawd */
        if (xe > SP_FBITS) {
@@ -97,7 +100,7 @@ int ieee754sp_tint(union ieee754sp x)
                if ((xm >> 31) != 0) {
                        /* This can happen after rounding */
                        ieee754_setcx(IEEE754_INVALID_OPERATION);
-                       return ieee754si_indef();
+                       return ieee754si_overflow(xs);
                }
                if (round || sticky)
                        ieee754_setcx(IEEE754_INEXACT);

diff --git a/arch/mips/math-emu/sp_tlong.c b/arch/mips/math-emu/sp_tlong.c
index 9f3c742..a2450c7 100644 (file)
--- a/arch/mips/math-emu/sp_tlong.c
+++ b/arch/mips/math-emu/sp_tlong.c
@@ -39,10 +39,13 @@ s64 ieee754sp_tlong(union ieee754sp x)
        switch (xc) {
        case IEEE754_CLASS_SNAN:
        case IEEE754_CLASS_QNAN:
-       case IEEE754_CLASS_INF:
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754di_indef();
 
+       case IEEE754_CLASS_INF:
+               ieee754_setcx(IEEE754_INVALID_OPERATION);
+               return ieee754di_overflow(xs);
+
        case IEEE754_CLASS_ZERO:
                return 0;
 
@@ -57,7 +60,7 @@ s64 ieee754sp_tlong(union ieee754sp x)
                /* Set invalid. We will only use overflow for floating
                   point overflow */
                ieee754_setcx(IEEE754_INVALID_OPERATION);
-               return ieee754di_indef();
+               return ieee754di_overflow(xs);
        }
        /* oh gawd */
        if (xe > SP_FBITS) {
@@ -94,7 +97,7 @@ s64 ieee754sp_tlong(union ieee754sp x)
                if ((xm >> 63) != 0) {
                        /* This can happen after rounding */
                        ieee754_setcx(IEEE754_INVALID_OPERATION);
-                       return ieee754di_indef();
+                       return ieee754di_overflow(xs);
                }
                if (round || sticky)
                        ieee754_setcx(IEEE754_INEXACT);