soft-float: add float32_log2() and float64_log2()

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6518 c046a42c-6fe2-441c-8c8c-71466251a162

2 files changed, 95 insertions, 0 deletions

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 3d5169d..4d58744 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -2057,6 +2057,53 @@ float32 float32_sqrt( float32 a STATUS_PARAM )
 }
 
 /*----------------------------------------------------------------------------
+| Returns the binary log of the single-precision floating-point value `a'.
+| The operation is performed according to the IEC/IEEE Standard for Binary
+| Floating-Point Arithmetic.
+*----------------------------------------------------------------------------*/
+float32 float32_log2( float32 a STATUS_PARAM )
+{
+    flag aSign, zSign;
+    int16 aExp;
+    bits32 aSig, zSig, i;
+
+    aSig = extractFloat32Frac( a );
+    aExp = extractFloat32Exp( a );
+    aSign = extractFloat32Sign( a );
+
+    if ( aExp == 0 ) {
+        if ( aSig == 0 ) return packFloat32( 1, 0xFF, 0 );
+        normalizeFloat32Subnormal( aSig, &aExp, &aSig );
+    }
+    if ( aSign ) {
+        float_raise( float_flag_invalid STATUS_VAR);
+        return float32_default_nan;
+    }
+    if ( aExp == 0xFF ) {
+        if ( aSig ) return propagateFloat32NaN( a, float32_zero STATUS_VAR );
+        return a;
+    }
+
+    aExp -= 0x7F;
+    aSig |= 0x00800000;
+    zSign = aExp < 0;
+    zSig = aExp << 23;
+
+    for (i = 1 << 22; i > 0; i >>= 1) {
+        aSig = ( (bits64)aSig * aSig ) >> 23;
+        if ( aSig & 0x01000000 ) {
+            aSig >>= 1;
+            zSig |= i;
+        }
+    }
+
+    if ( zSign )
+        zSig = -zSig;
+
+    return normalizeRoundAndPackFloat32( zSign, 0x85, zSig STATUS_VAR );
+}
+
+/*----------------------------------------------------------------------------
 | Returns 1 if the single-precision floating-point value `a' is equal to
 | the corresponding value `b', and 0 otherwise.  The comparison is performed
 | according to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
@@ -3006,6 +3053,52 @@ float64 float64_sqrt( float64 a STATUS_PARAM )
 }
 
 /*----------------------------------------------------------------------------
+| Returns the binary log of the double-precision floating-point value `a'.
+| The operation is performed according to the IEC/IEEE Standard for Binary
+| Floating-Point Arithmetic.
+*----------------------------------------------------------------------------*/
+float64 float64_log2( float64 a STATUS_PARAM )
+{
+    flag aSign, zSign;
+    int16 aExp;
+    bits64 aSig, aSig0, aSig1, zSig, i;
+
+    aSig = extractFloat64Frac( a );
+    aExp = extractFloat64Exp( a );
+    aSign = extractFloat64Sign( a );
+
+    if ( aExp == 0 ) {
+        if ( aSig == 0 ) return packFloat64( 1, 0x7FF, 0 );
+        normalizeFloat64Subnormal( aSig, &aExp, &aSig );
+    }
+    if ( aSign ) {
+        float_raise( float_flag_invalid STATUS_VAR);
+        return float64_default_nan;
+    }
+    if ( aExp == 0x7FF ) {
+        if ( aSig ) return propagateFloat64NaN( a, float64_zero STATUS_VAR );
+        return a;
+    }
+
+    aExp -= 0x3FF;
+    aSig |= LIT64( 0x0010000000000000 );
+    zSign = aExp < 0;
+    zSig = (bits64)aExp << 52;
+    for (i = 1LL << 51; i > 0; i >>= 1) {
+        mul64To128( aSig, aSig, &aSig0, &aSig1 );
+        aSig = ( aSig0 << 12 ) | ( aSig1 >> 52 );
+        if ( aSig & LIT64( 0x0020000000000000 ) ) {
+            aSig >>= 1;
+            zSig |= i;
+        }
+    }
+
+    if ( zSign )
+        zSig = -zSig;
+    return normalizeRoundAndPackFloat64( zSign, 0x408, zSig STATUS_VAR );
+}
+
+/*----------------------------------------------------------------------------
 | Returns 1 if the double-precision floating-point value `a' is equal to the
 | corresponding value `b', and 0 otherwise.  The comparison is performed
 | according to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
diff --git a/fpu/softfloat.h b/fpu/softfloat.h
index a06a313..a0353da 100644
--- a/fpu/softfloat.h
+++ b/fpu/softfloat.h
@@ -269,6 +269,7 @@ float32 float32_mul( float32, float32 STATUS_PARAM );
 float32 float32_div( float32, float32 STATUS_PARAM );
 float32 float32_rem( float32, float32 STATUS_PARAM );
 float32 float32_sqrt( float32 STATUS_PARAM );
+float32 float32_log2( float32 STATUS_PARAM );
 int float32_eq( float32, float32 STATUS_PARAM );
 int float32_le( float32, float32 STATUS_PARAM );
 int float32_lt( float32, float32 STATUS_PARAM );
@@ -339,6 +340,7 @@ float64 float64_mul( float64, float64 STATUS_PARAM );
 float64 float64_div( float64, float64 STATUS_PARAM );
 float64 float64_rem( float64, float64 STATUS_PARAM );
 float64 float64_sqrt( float64 STATUS_PARAM );
+float64 float64_log2( float64 STATUS_PARAM );
 int float64_eq( float64, float64 STATUS_PARAM );
 int float64_le( float64, float64 STATUS_PARAM );
 int float64_lt( float64, float64 STATUS_PARAM );