[Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

From: Petar Jovanovic <petar.jovanovic@imgtec.com>

This change corrects rounding and saturation of Q31 fractional value in
mipsdsp_trunc16_sat16_round(). Overflow detection was incorrect for the
corner case for PRECRQ_RS.PH, and this test case is also part of the change.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
---
 target-mips/dsp_helper.c                   |   12 ++++++------
 tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c |   24 ++++++++++++++++++++----
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/target-mips/dsp_helper.c b/target-mips/dsp_helper.c
index 4116de9..306b332 100644
--- a/target-mips/dsp_helper.c
+++ b/target-mips/dsp_helper.c
@@ -648,16 +648,16 @@ static inline int32_t mipsdsp_sat16_mul_q15_q15(uint16_t a, uint16_t b,
 static inline uint16_t mipsdsp_trunc16_sat16_round(int32_t a,
                                                    CPUMIPSState *env)
 {
-    int64_t temp;
-
-    temp = (int32_t)a + 0x00008000;
+    uint16_t temp;
 
-    if (a > (int)0x7fff8000) {
-        temp = 0x7FFFFFFF;
+    if (a > 0x7FFF7FFF) {
+        temp = 0x7FFF;
         set_DSPControl_overflow_flag(1, 22, env);
+    } else {
+        temp = ((a + 0x8000) >> 16) & 0xFFFF;
     }
 
-    return (temp >> 16) & 0xFFFF;
+    return temp;
 }
 
 static inline uint8_t mipsdsp_sat8_reduce_precision(uint16_t a,
diff --git a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
index 3535b37..da6845b 100644
--- a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
+++ b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
@@ -12,18 +12,34 @@ int main()
     result = 0x12348765;
 
     __asm
-        ("precrq_rs.ph.w %0, %1, %2\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %1, %2\n\t"
          : "=r"(rd)
          : "r"(rs), "r"(rt)
         );
     assert(result == rd);
 
-    rs = 0x7fffC678;
+    rs = 0x7FFFC678;
     rt = 0x865432A0;
-    result = 0x7fff8654;
+    result = 0x7FFF8654;
 
     __asm
-        ("precrq_rs.ph.w %0, %2, %3\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
+         "rddsp %1\n\t"
+         : "=r"(rd), "=r"(dsp)
+         : "r"(rs), "r"(rt)
+        );
+    assert(((dsp >> 22) & 0x01) == 1);
+    assert(result == rd);
+
+    rs = 0xBEEFFEED;
+    rt = 0x7FFF8000;
+    result = 0xBEF07FFF;
+
+    __asm
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
          "rddsp %1\n\t"
          : "=r"(rd), "=r"(dsp)
          : "r"(rs), "r"(rt)
-- 
1.7.9.5

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

ping

http://patchwork.ozlabs.org/patch/245624/
________________________________________
From: Petar Jovanovic [petar.jovanovic@rt-rk.com]
Sent: Wednesday, May 22, 2013 3:35 PM
To: qemu-devel@nongnu.org
Cc: Petar Jovanovic; aurelien@aurel32.net
Subject: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

From: Petar Jovanovic <petar.jovanovic@imgtec.com>

This change corrects rounding and saturation of Q31 fractional value in
mipsdsp_trunc16_sat16_round(). Overflow detection was incorrect for the
corner case for PRECRQ_RS.PH, and this test case is also part of the change.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
---
 target-mips/dsp_helper.c                   |   12 ++++++------
 tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c |   24 ++++++++++++++++++++----
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/target-mips/dsp_helper.c b/target-mips/dsp_helper.c
index 4116de9..306b332 100644
--- a/target-mips/dsp_helper.c
+++ b/target-mips/dsp_helper.c
@@ -648,16 +648,16 @@ static inline int32_t mipsdsp_sat16_mul_q15_q15(uint16_t a, uint16_t b,
 static inline uint16_t mipsdsp_trunc16_sat16_round(int32_t a,
                                                    CPUMIPSState *env)
 {
-    int64_t temp;
-
-    temp = (int32_t)a + 0x00008000;
+    uint16_t temp;

-    if (a > (int)0x7fff8000) {
-        temp = 0x7FFFFFFF;
+    if (a > 0x7FFF7FFF) {
+        temp = 0x7FFF;
         set_DSPControl_overflow_flag(1, 22, env);
+    } else {
+        temp = ((a + 0x8000) >> 16) & 0xFFFF;
     }

-    return (temp >> 16) & 0xFFFF;
+    return temp;
 }

 static inline uint8_t mipsdsp_sat8_reduce_precision(uint16_t a,
diff --git a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
index 3535b37..da6845b 100644
--- a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
+++ b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
@@ -12,18 +12,34 @@ int main()
     result = 0x12348765;

     __asm
-        ("precrq_rs.ph.w %0, %1, %2\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %1, %2\n\t"
          : "=r"(rd)
          : "r"(rs), "r"(rt)
         );
     assert(result == rd);

-    rs = 0x7fffC678;
+    rs = 0x7FFFC678;
     rt = 0x865432A0;
-    result = 0x7fff8654;
+    result = 0x7FFF8654;

     __asm
-        ("precrq_rs.ph.w %0, %2, %3\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
+         "rddsp %1\n\t"
+         : "=r"(rd), "=r"(dsp)
+         : "r"(rs), "r"(rt)
+        );
+    assert(((dsp >> 22) & 0x01) == 1);
+    assert(result == rd);
+
+    rs = 0xBEEFFEED;
+    rt = 0x7FFF8000;
+    result = 0xBEF07FFF;
+
+    __asm
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
          "rddsp %1\n\t"
          : "=r"(rd), "=r"(dsp)
          : "r"(rs), "r"(rt)
--
1.7.9.5

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

ping
________________________________________
From: Petar Jovanovic
Sent: Sunday, June 09, 2013 4:34 AM
To: Petar Jovanovic; qemu-devel@nongnu.org
Cc: aurelien@aurel32.net
Subject: RE: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

ping

http://patchwork.ozlabs.org/patch/245624/
________________________________________
From: Petar Jovanovic [petar.jovanovic@rt-rk.com]
Sent: Wednesday, May 22, 2013 3:35 PM
To: qemu-devel@nongnu.org
Cc: Petar Jovanovic; aurelien@aurel32.net
Subject: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

From: Petar Jovanovic <petar.jovanovic@imgtec.com>

This change corrects rounding and saturation of Q31 fractional value in
mipsdsp_trunc16_sat16_round(). Overflow detection was incorrect for the
corner case for PRECRQ_RS.PH, and this test case is also part of the change.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
---
 target-mips/dsp_helper.c                   |   12 ++++++------
 tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c |   24 ++++++++++++++++++++----
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/target-mips/dsp_helper.c b/target-mips/dsp_helper.c
index 4116de9..306b332 100644
--- a/target-mips/dsp_helper.c
+++ b/target-mips/dsp_helper.c
@@ -648,16 +648,16 @@ static inline int32_t mipsdsp_sat16_mul_q15_q15(uint16_t a, uint16_t b,
 static inline uint16_t mipsdsp_trunc16_sat16_round(int32_t a,
                                                    CPUMIPSState *env)
 {
-    int64_t temp;
-
-    temp = (int32_t)a + 0x00008000;
+    uint16_t temp;

-    if (a > (int)0x7fff8000) {
-        temp = 0x7FFFFFFF;
+    if (a > 0x7FFF7FFF) {
+        temp = 0x7FFF;
         set_DSPControl_overflow_flag(1, 22, env);
+    } else {
+        temp = ((a + 0x8000) >> 16) & 0xFFFF;
     }

-    return (temp >> 16) & 0xFFFF;
+    return temp;
 }

 static inline uint8_t mipsdsp_sat8_reduce_precision(uint16_t a,
diff --git a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
index 3535b37..da6845b 100644
--- a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
+++ b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
@@ -12,18 +12,34 @@ int main()
     result = 0x12348765;

     __asm
-        ("precrq_rs.ph.w %0, %1, %2\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %1, %2\n\t"
          : "=r"(rd)
          : "r"(rs), "r"(rt)
         );
     assert(result == rd);

-    rs = 0x7fffC678;
+    rs = 0x7FFFC678;
     rt = 0x865432A0;
-    result = 0x7fff8654;
+    result = 0x7FFF8654;

     __asm
-        ("precrq_rs.ph.w %0, %2, %3\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
+         "rddsp %1\n\t"
+         : "=r"(rd), "=r"(dsp)
+         : "r"(rs), "r"(rt)
+        );
+    assert(((dsp >> 22) & 0x01) == 1);
+    assert(result == rd);
+
+    rs = 0xBEEFFEED;
+    rt = 0x7FFF8000;
+    result = 0xBEF07FFF;
+
+    __asm
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
          "rddsp %1\n\t"
          : "=r"(rd), "=r"(dsp)
          : "r"(rs), "r"(rt)
--
1.7.9.5

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

ping
________________________________________
From: Petar Jovanovic
Sent: Tuesday, June 18, 2013 12:39 AM
To: Petar Jovanovic; qemu-devel@nongnu.org
Cc: aurelien@aurel32.net
Subject: RE: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

ping
________________________________________
From: Petar Jovanovic
Sent: Sunday, June 09, 2013 4:34 AM
To: Petar Jovanovic; qemu-devel@nongnu.org
Cc: aurelien@aurel32.net
Subject: RE: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

ping

http://patchwork.ozlabs.org/patch/245624/
________________________________________
From: Petar Jovanovic [petar.jovanovic@rt-rk.com]
Sent: Wednesday, May 22, 2013 3:35 PM
To: qemu-devel@nongnu.org
Cc: Petar Jovanovic; aurelien@aurel32.net
Subject: [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

From: Petar Jovanovic <petar.jovanovic@imgtec.com>

This change corrects rounding and saturation of Q31 fractional value in
mipsdsp_trunc16_sat16_round(). Overflow detection was incorrect for the
corner case for PRECRQ_RS.PH, and this test case is also part of the change.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
---
 target-mips/dsp_helper.c                   |   12 ++++++------
 tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c |   24 ++++++++++++++++++++----
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/target-mips/dsp_helper.c b/target-mips/dsp_helper.c
index 4116de9..306b332 100644
--- a/target-mips/dsp_helper.c
+++ b/target-mips/dsp_helper.c
@@ -648,16 +648,16 @@ static inline int32_t mipsdsp_sat16_mul_q15_q15(uint16_t a, uint16_t b,
 static inline uint16_t mipsdsp_trunc16_sat16_round(int32_t a,
                                                    CPUMIPSState *env)
 {
-    int64_t temp;
-
-    temp = (int32_t)a + 0x00008000;
+    uint16_t temp;

-    if (a > (int)0x7fff8000) {
-        temp = 0x7FFFFFFF;
+    if (a > 0x7FFF7FFF) {
+        temp = 0x7FFF;
         set_DSPControl_overflow_flag(1, 22, env);
+    } else {
+        temp = ((a + 0x8000) >> 16) & 0xFFFF;
     }

-    return (temp >> 16) & 0xFFFF;
+    return temp;
 }

 static inline uint8_t mipsdsp_sat8_reduce_precision(uint16_t a,
diff --git a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
index 3535b37..da6845b 100644
--- a/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
+++ b/tests/tcg/mips/mips32-dsp/precrq_rs_ph_w.c
@@ -12,18 +12,34 @@ int main()
     result = 0x12348765;

     __asm
-        ("precrq_rs.ph.w %0, %1, %2\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %1, %2\n\t"
          : "=r"(rd)
          : "r"(rs), "r"(rt)
         );
     assert(result == rd);

-    rs = 0x7fffC678;
+    rs = 0x7FFFC678;
     rt = 0x865432A0;
-    result = 0x7fff8654;
+    result = 0x7FFF8654;

     __asm
-        ("precrq_rs.ph.w %0, %2, %3\n\t"
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
+         "rddsp %1\n\t"
+         : "=r"(rd), "=r"(dsp)
+         : "r"(rs), "r"(rt)
+        );
+    assert(((dsp >> 22) & 0x01) == 1);
+    assert(result == rd);
+
+    rs = 0xBEEFFEED;
+    rt = 0x7FFF8000;
+    result = 0xBEF07FFF;
+
+    __asm
+        ("wrdsp $0\n\t"
+         "precrq_rs.ph.w %0, %2, %3\n\t"
          "rddsp %1\n\t"
          : "=r"(rd), "=r"(dsp)
          : "r"(rs), "r"(rt)
--
1.7.9.5

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Richard Henderson]

On 06/17/2013 03:39 PM, Petar Jovanovic wrote:
> -    int64_t temp;
> -
> -    temp = (int32_t)a + 0x00008000;
> +    uint16_t temp;
> 
> -    if (a > (int)0x7fff8000) {
> -        temp = 0x7FFFFFFF;
> +    if (a > 0x7FFF7FFF) {
> +        temp = 0x7FFF;
>          set_DSPControl_overflow_flag(1, 22, env);
> +    } else {
> +        temp = ((a + 0x8000) >> 16) & 0xFFFF;

This doesn't look right either, as it doesn't properly check for overflow of
negative values.  I'd feel better if we implement this function exactly as
documented, modulo actually using 64-bit arithmetic.  How about

  int32_t temp;

  /* Shift right by one, to avoid needing 64-bit arithmetic.  As this A is
     signed, this creates the copy of the sign bit as documented.  */
  a >>= 1;
  temp = a + 0x4000;

  /* Compare temp{31} with temp{30} by xoring into the sign bit.  */
  if ((temp ^ (temp << 1)) < 0) {
      set_DSPControl_overflow_flag(1, 22, env);
      return 0x7fff;
  }
  return temp >> 15;


r~

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

________________________________________
From: Richard Henderson [rth7680@gmail.com] on behalf of Richard Henderson [rth@twiddle.net]
Sent: Thursday, June 27, 2013 8:20 PM
To: Petar Jovanovic
Cc: Petar Jovanovic; qemu-devel@nongnu.org; aurelien@aurel32.net
Subject: Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

On 06/17/2013 03:39 PM, Petar Jovanovic wrote:
> -    int64_t temp;
> -
> -    temp = (int32_t)a + 0x00008000;
> +    uint16_t temp;
>
> -    if (a > (int)0x7fff8000) {
> -        temp = 0x7FFFFFFF;
> +    if (a > 0x7FFF7FFF) {
> +        temp = 0x7FFF;
>          set_DSPControl_overflow_flag(1, 22, env);
> +    } else {
> +        temp = ((a + 0x8000) >> 16) & 0xFFFF;

> This doesn't look right either, as it doesn't properly check for overflow of
> negative values.

What overflow of negative values?
Can you please list the values for which the result would not be correct?

Thanks.

Petar

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Richard Henderson]

On 06/27/2013 02:48 PM, Petar Jovanovic wrote:
>> This doesn't look right either, as it doesn't properly check for overflow of
>> negative values.
> 
> What overflow of negative values?
> Can you please list the values for which the result would not be correct?

Hmm, I suppose since we're always rounding to +INF, we can't
overflow in the negative direction.  The patch could use some
commentary along those lines...


r~

Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

[Petar Jovanovic]

________________________________________
From: Richard Henderson [rth7680@gmail.com] on behalf of Richard Henderson [rth@twiddle.net]
Sent: Friday, June 28, 2013 7:40 PM
To: Petar Jovanovic
Cc: Petar Jovanovic; qemu-devel@nongnu.org; aurelien@aurel32.net
Subject: Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round

On 06/27/2013 02:48 PM, Petar Jovanovic wrote:
>> This doesn't look right either, as it doesn't properly check for overflow of
>> negative values.
>
> What overflow of negative values?
> Can you please list the values for which the result would not be correct?

> Hmm, I suppose since we're always rounding to +INF, we can't
> overflow in the negative direction.  The patch could use some
> commentary along those lines...
> r~

Ok, I will add comments in the code and resubmit the patch.

Petar