[Qemu-devel] [PATCH] fpu/softfloat: Replace countLeadingZeros32/64 with clz32/64

[Thomas Huth]

Our minimum required compiler for compiling QEMU is GCC 4.1 these days,
so we can drop the support for compilers which do not provide the
__builtin_clz*() functions yet. Since the countLeadingZeros32/64 are
then identical to the clz32/64 functions, and we do not have to sync
the softloat 2 codebase with upstream anymore (softloat 3 is a complete
rewrite) we can simply replace the functions with our QEMU versions.

Suggested-by: Peter Maydell <address@hidden>
Signed-off-by: Thomas Huth <address@hidden>
---
 fpu/softfloat.c                | 26 ++++++-------
 include/fpu/softfloat-macros.h | 87 ------------------------------------------
 2 files changed, 13 insertions(+), 100 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 8b91cd6..25a8dd9 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -2681,7 +2681,7 @@ static void
 {
     int8_t shiftCount;
 
-    shiftCount = countLeadingZeros32( aSig ) - 8;
+    shiftCount = clz32(aSig) - 8;
     *zSigPtr = aSig<<shiftCount;
     *zExpPtr = 1 - shiftCount;
 
@@ -2789,7 +2789,7 @@ static float32
 {
     int8_t shiftCount;
 
-    shiftCount = countLeadingZeros32( zSig ) - 1;
+    shiftCount = clz32(zSig) - 1;
     return roundAndPackFloat32(zSign, zExp - shiftCount, zSig<<shiftCount,
                                status);
 
@@ -2822,7 +2822,7 @@ static void
 {
     int8_t shiftCount;
 
-    shiftCount = countLeadingZeros64( aSig ) - 11;
+    shiftCount = clz64(aSig) - 11;
     *zSigPtr = aSig<<shiftCount;
     *zExpPtr = 1 - shiftCount;
 
@@ -2960,7 +2960,7 @@ static float64
 {
     int8_t shiftCount;
 
-    shiftCount = countLeadingZeros64( zSig ) - 1;
+    shiftCount = clz64(zSig) - 1;
     return roundAndPackFloat64(zSign, zExp - shiftCount, zSig<<shiftCount,
                                status);
 
@@ -2978,7 +2978,7 @@ void normalizeFloatx80Subnormal(uint64_t aSig, int32_t 
*zExpPtr,
 {
     int8_t shiftCount;
 
-    shiftCount = countLeadingZeros64( aSig );
+    shiftCount = clz64(aSig);
     *zSigPtr = aSig<<shiftCount;
     *zExpPtr = 1 - shiftCount;
 }
@@ -3217,7 +3217,7 @@ floatx80 normalizeRoundAndPackFloatx80(int8_t 
roundingPrecision,
         zSig1 = 0;
         zExp -= 64;
     }
-    shiftCount = countLeadingZeros64( zSig0 );
+    shiftCount = clz64(zSig0);
     shortShift128Left( zSig0, zSig1, shiftCount, &zSig0, &zSig1 );
     zExp -= shiftCount;
     return roundAndPackFloatx80(roundingPrecision, zSign, zExp,
@@ -3294,7 +3294,7 @@ static void
     int8_t shiftCount;
 
     if ( aSig0 == 0 ) {
-        shiftCount = countLeadingZeros64( aSig1 ) - 15;
+        shiftCount = clz64(aSig1) - 15;
         if ( shiftCount < 0 ) {
             *zSig0Ptr = aSig1>>( - shiftCount );
             *zSig1Ptr = aSig1<<( shiftCount & 63 );
@@ -3306,7 +3306,7 @@ static void
         *zExpPtr = - shiftCount - 63;
     }
     else {
-        shiftCount = countLeadingZeros64( aSig0 ) - 15;
+        shiftCount = clz64(aSig0) - 15;
         shortShift128Left( aSig0, aSig1, shiftCount, zSig0Ptr, zSig1Ptr );
         *zExpPtr = 1 - shiftCount;
     }
@@ -3495,7 +3495,7 @@ static float128 normalizeRoundAndPackFloat128(flag zSign, 
int32_t zExp,
         zSig1 = 0;
         zExp -= 64;
     }
-    shiftCount = countLeadingZeros64( zSig0 ) - 15;
+    shiftCount = clz64(zSig0) - 15;
     if ( 0 <= shiftCount ) {
         zSig2 = 0;
         shortShift128Left( zSig0, zSig1, shiftCount, &zSig0, &zSig1 );
@@ -3527,7 +3527,7 @@ floatx80 int32_to_floatx80(int32_t a, float_status 
*status)
     if ( a == 0 ) return packFloatx80( 0, 0, 0 );
     zSign = ( a < 0 );
     absA = zSign ? - a : a;
-    shiftCount = countLeadingZeros32( absA ) + 32;
+    shiftCount = clz32(absA) + 32;
     zSig = absA;
     return packFloatx80( zSign, 0x403E - shiftCount, zSig<<shiftCount );
 
@@ -3549,7 +3549,7 @@ float128 int32_to_float128(int32_t a, float_status 
*status)
     if ( a == 0 ) return packFloat128( 0, 0, 0, 0 );
     zSign = ( a < 0 );
     absA = zSign ? - a : a;
-    shiftCount = countLeadingZeros32( absA ) + 17;
+    shiftCount = clz32(absA) + 17;
     zSig0 = absA;
     return packFloat128( zSign, 0x402E - shiftCount, zSig0<<shiftCount, 0 );
 
@@ -3571,7 +3571,7 @@ floatx80 int64_to_floatx80(int64_t a, float_status 
*status)
     if ( a == 0 ) return packFloatx80( 0, 0, 0 );
     zSign = ( a < 0 );
     absA = zSign ? - a : a;
-    shiftCount = countLeadingZeros64( absA );
+    shiftCount = clz64(absA);
     return packFloatx80( zSign, 0x403E - shiftCount, absA<<shiftCount );
 
 }
@@ -3593,7 +3593,7 @@ float128 int64_to_float128(int64_t a, float_status 
*status)
     if ( a == 0 ) return packFloat128( 0, 0, 0, 0 );
     zSign = ( a < 0 );
     absA = zSign ? - a : a;
-    shiftCount = countLeadingZeros64( absA ) + 49;
+    shiftCount = clz64(absA) + 49;
     zExp = 0x406E - shiftCount;
     if ( 64 <= shiftCount ) {
         zSig1 = 0;
diff --git a/include/fpu/softfloat-macros.h b/include/fpu/softfloat-macros.h
index 35e1603..edc6821 100644
--- a/include/fpu/softfloat-macros.h
+++ b/include/fpu/softfloat-macros.h
@@ -80,17 +80,6 @@ this code that are retained.
  */
 
 /*----------------------------------------------------------------------------
-| This macro tests for minimum version of the GNU C compiler.
-*----------------------------------------------------------------------------*/
-#if defined(__GNUC__) && defined(__GNUC_MINOR__)
-# define SOFTFLOAT_GNUC_PREREQ(maj, min) \
-         ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
-#else
-# define SOFTFLOAT_GNUC_PREREQ(maj, min) 0
-#endif
-
-
-/*----------------------------------------------------------------------------
 | Shifts `a' right by the number of bits given in `count'.  If any nonzero
 | bits are shifted off, they are ``jammed'' into the least significant bit of
 | the result by setting the least significant bit to 1.  The value of `count'
@@ -713,82 +702,6 @@ static inline uint32_t estimateSqrt32(int aExp, uint32_t a)
 }
 
 /*----------------------------------------------------------------------------
-| Returns the number of leading 0 bits before the most-significant 1 bit of
-| `a'.  If `a' is zero, 32 is returned.
-*----------------------------------------------------------------------------*/
-
-static inline int8_t countLeadingZeros32(uint32_t a)
-{
-#if SOFTFLOAT_GNUC_PREREQ(3, 4)
-    if (a) {
-        return __builtin_clz(a);
-    } else {
-        return 32;
-    }
-#else
-    static const int8_t countLeadingZerosHigh[] = {
-        8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
-        3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
-        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-    };
-    int8_t shiftCount;
-
-    shiftCount = 0;
-    if ( a < 0x10000 ) {
-        shiftCount += 16;
-        a <<= 16;
-    }
-    if ( a < 0x1000000 ) {
-        shiftCount += 8;
-        a <<= 8;
-    }
-    shiftCount += countLeadingZerosHigh[ a>>24 ];
-    return shiftCount;
-#endif
-}
-
-/*----------------------------------------------------------------------------
-| Returns the number of leading 0 bits before the most-significant 1 bit of
-| `a'.  If `a' is zero, 64 is returned.
-*----------------------------------------------------------------------------*/
-
-static inline int8_t countLeadingZeros64(uint64_t a)
-{
-#if SOFTFLOAT_GNUC_PREREQ(3, 4)
-    if (a) {
-        return __builtin_clzll(a);
-    } else {
-        return 64;
-    }
-#else
-    int8_t shiftCount;
-
-    shiftCount = 0;
-    if ( a < ( (uint64_t) 1 )<<32 ) {
-        shiftCount += 32;
-    }
-    else {
-        a >>= 32;
-    }
-    shiftCount += countLeadingZeros32( a );
-    return shiftCount;
-#endif
-}
-
-/*----------------------------------------------------------------------------
 | Returns 1 if the 128-bit value formed by concatenating `a0' and `a1'
 | is equal to the 128-bit value formed by concatenating `b0' and `b1'.
 | Otherwise, returns 0.
-- 
1.8.3.1