Fixing bf32_to_bf16 conversions

3 files changed, 68 insertions, 3 deletions

diff --git a/source/bf16_to_f32.c b/source/bf16_to_f32.c
index a30006a..a76632e 100644
--- a/source/bf16_to_f32.c
+++ b/source/bf16_to_f32.c
@@ -85,7 +85,7 @@ float32_t bf16_to_f32( bfloat16_t a )
     }
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
-    uiZ = packToF32UI( sign, exp, (uint_fast32_t) frac<<16 );
+    uiZ = packToF32UI( sign, exp, ((uint_fast32_t) frac) <<16 );
  uiZ:
     uZ.ui = uiZ;
     return uZ.f;
diff --git a/source/f32_to_bf16.c b/source/f32_to_bf16.c
index 059e05a..6f81493 100644
--- a/source/f32_to_bf16.c
+++ b/source/f32_to_bf16.c
@@ -41,6 +41,9 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "specialize.h"
 #include "softfloat.h"
 
+#include <inttypes.h>
+#include <stdio.h>
+
 bfloat16_t f32_to_bf16( float32_t a )
 {
     union ui32_f32 uA;
@@ -75,7 +78,8 @@ bfloat16_t f32_to_bf16( float32_t a )
     }
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
-    // frac is a 24-bit mantissa, right shifted by 
+    // frac is a 24-bit mantissa, right shifted by 9
+    // In the normal case, (24-9) = 15 are set 
     frac16 = frac>>9 | ((frac & 0x1FF) != 0);
     if ( ! (exp | frac16) ) {
         uiZ = packToBF16UI( sign, 0, 0 );
@@ -83,7 +87,16 @@ bfloat16_t f32_to_bf16( float32_t a )
     }
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
-    return softfloat_roundPackToBF16( sign, exp, frac16 | 0x4000 );
+    // softfloat_roundPackToBF16 exponent argument (2nd argument)
+    // must correspond to the exponent of fracIn[13] bits
+    // (fracIn is the 3rd and last argument) 
+    uint_fast32_t mask = exp ? 0x4000 : 0x0; // implicit one mask added if input is a normal number
+    // exponent for the lowest normal and largest subnormal should be equal
+    // but is not in IEEE encoding so mantissa must be partially normalized
+    // (by one bit) for subnormal numbers. Such that (exp - 1) corresponds
+    // to the exponent of frac16[13]
+    frac16 = frac16 << (exp ? 0 : 1);
+    return softfloat_roundPackToBF16( sign, exp - 1, frac16 | mask );
  uiZ:
     uZ.ui = uiZ;
     return uZ.f;
diff --git a/source/s_normSubnormalBF16Sig.c b/source/s_normSubnormalBF16Sig.c
new file mode 100644
index 0000000..b81baa9
--- /dev/null
+++ b/source/s_normSubnormalBF16Sig.c
@@ -0,0 +1,52 @@
+
+/*============================================================================
+
+This C source file is part of the SoftFloat IEEE Floating-Point Arithmetic
+Package, Release 3e, by John R. Hauser.
+
+Copyright 2011, 2012, 2013, 2014, 2015, 2016 The Regents of the University of
+California.  All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+ 1. Redistributions of source code must retain the above copyright notice,
+    this list of conditions, and the following disclaimer.
+
+ 2. Redistributions in binary form must reproduce the above copyright notice,
+    this list of conditions, and the following disclaimer in the documentation
+    and/or other materials provided with the distribution.
+
+ 3. Neither the name of the University nor the names of its contributors may
+    be used to endorse or promote products derived from this software without
+    specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS", AND ANY
+EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
+DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+=============================================================================*/
+
+#include <stdint.h>
+#include "platform.h"
+#include "internals.h"
+
+struct exp8_sig16 softfloat_normSubnormalBF16Sig( uint_fast16_t sig )
+{
+    int_fast8_t shiftDist;
+    struct exp8_sig16 z;
+
+    shiftDist = softfloat_countLeadingZeros16( sig ) - 8;
+    z.exp = 1 - shiftDist;
+    z.sig = sig<<shiftDist;
+    return z;
+
+}
+