target-mips: fix multiplication in mipsdsp_rndq15_mul_q15_q15

Multiplication of Q15 fractional halfword vectors was incorrect in the
previous implementation of mipsdsp_rndq15_mul_q15_q15. It failed to take
element signs into account. This change fixes it, and it adds a test case
for it.

The change also removes unnecessary cast in the function
mipsdsp_mul_q15_q15_overflowflag21().

Signed-off-by: Petar Jovanovic <[email protected]>
Reviewed-by: Richard Henderson  <[email protected]> 
Signed-off-by: Aurelien Jarno <[email protected]>

target-mips/dsp_helper.c

@@ -390,7 +390,7 @@ static inline int32_t mipsdsp_mul_q15_q15_overflowflag21(uint16_t a, uint16_t b,
         temp = 0x7FFFFFFF;
         set_DSPControl_overflow_flag(1, 21, env);
     } else {
-        temp = ((int32_t)(int16_t)a * (int32_t)(int16_t)b) << 1;
+        temp = ((int16_t)a * (int16_t)b) << 1;
     }
 
     return temp;
@@ -622,7 +622,7 @@ static inline int16_t mipsdsp_rndq15_mul_q15_q15(uint16_t a, uint16_t b,
         temp = 0x7FFF0000;
         set_DSPControl_overflow_flag(1, 21, env);
     } else {
-        temp = (a * b) << 1;
+        temp = ((int16_t)a * (int16_t)b) << 1;
         temp = temp + 0x00008000;
     }
 

tests/tcg/mips/mips32-dsp/mulq_rs_ph.c

@@ -12,7 +12,24 @@ int main()
     resultdsp = 1;
 
     __asm
-        ("mulq_rs.ph %0, %2, %3\n\t"
+        ("wrdsp $0\n\t"
+         "mulq_rs.ph %0, %2, %3\n\t"
+         "rddsp %1\n\t"
+         : "=r"(rd), "=r"(dsp)
+         : "r"(rs), "r"(rt)
+        );
+    dsp = (dsp >> 21) & 0x01;
+    assert(rd  == result);
+    assert(dsp == resultdsp);
+
+    rs = 0x80011234;
+    rt = 0x80024321;
+    result = 0x7FFD098C;
+    resultdsp = 0;
+
+    __asm
+        ("wrdsp $0\n\t"
+         "mulq_rs.ph %0, %2, %3\n\t"
          "rddsp %1\n\t"
          : "=r"(rd), "=r"(dsp)
          : "r"(rs), "r"(rt)