Cleanup donna_32.cpp arithmetic shift

1 files changed, 60 insertions, 35 deletions

diff --git a/donna_32.cpp b/donna_32.cpp
index e290f41f..ffcf5558 100644
--- a/donna_32.cpp
+++ b/donna_32.cpp
@@ -56,10 +56,9 @@
 #include "stdcpp.h"

 #include "cpu.h"

 

-// This macro is not in a header like config.h because

-// we don't want it exposed to user code. We also need

-// a standard header like <stdint.h> or <stdef.h>.

-// Langley uses uint128_t in the 64-bit code paths so

+// This macro is not in a header like config.h because we don't want it

+// exposed to user code. We also need a standard header like <stdint.h>

+// or <stdef.h>. Langley uses uint128_t in the 64-bit code paths so

 // we further restrict 64-bit code.

 #if (UINTPTR_MAX == 0xffffffff) || !defined(CRYPTOPP_WORD128_AVAILABLE)

 # define CRYPTOPP_32BIT 1

@@ -67,6 +66,16 @@
 # define CRYPTOPP_64BIT 1

 #endif

 

+// Some compilers don't handle the code for the arithmetic shifts well.

+// For compilers we know how to support we will issue the asm to sidestep

+// believe the problem. We also switch to a slightly different pattern.

+// We believe the pattern preserves the existing properties without a

+// branch. The ASM uses one intruction, while the C statement use 2 to 6

+// instructions, depending on the compiler.

+#if (__GNUC__ >= 3) || (__SUNPRO_CC >= 0x5100)

+# define CRYPTOPP_ASR_ASM 1

+#endif

+

 // Squash MS LNK4221 and libtool warnings

 extern const char DONNA32_FNAME[] = __FILE__;

 

@@ -84,41 +93,53 @@ using CryptoPP::sword64;
 typedef sword64 limb;

 

 // Added by JW for SunCC. Avoid the bit twiddling hacks.

+template <unsigned int S>

 inline int SignExtend(int val)

 {

-#if (__GNUC__ >= 3) || (__SUNPRO_CC >= 0x5100)

-# if CRYPTOPP_BOOL_X86

+#if defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_X86)

     __asm__

     (

-        "sar $31, %0      \n"

-        : "+g" (val) : : "cc"

+        "sar %1, %0    \n"

+        : "+g" (val) : "I" (S) : "cc"

     );

     return val;

-# endif

-// TODO: ARM

-#endif

-

+#elif defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_ARM32)

+    __asm__

+    (

+        "asr %0, %0, %1    \n"

+        : "+r" (val) : "I" (S) :

+    );

+    return val;

+#else

     // GCC and SunCC compile down to a shift and neg.

-    return (val >> 31) * -1;

+    // Also see the comments for CRYPTOPP_ASR_ASM.

+    return (val >> S) * -1;

+#endif

 }

 

-// Added by JW for SunCC. Avoid the bit twiddling hacks.

+template <unsigned int S>

 inline unsigned int SignExtend(unsigned int val)

 {

-#if (__GNUC__ >= 3) || (__SUNPRO_CC >= 0x5100)

-# if CRYPTOPP_BOOL_X86

+#if defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_X86)

     __asm__

     (

-        "sar $31, %0      \n"

-        : "+g" (val) : : "cc"

+        "sar %1, %0    \n"

+        : "+g" (val) : "I" (S) : "cc"

     );

     return val;

-# endif

-// TODO: ARM

-#endif

-

+#elif defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_ARM32)

+    __asm__

+    (

+        "asr %0, %0, %1    \n"

+        : "+r" (val) : "I" (S) :

+    );

+    return val;

+#else

     // GCC and SunCC compile down to a shift and neg.

-    return (unsigned int)(((signed int)(val >> 31)) * -1);

+    // Also see the comments for CRYPTOPP_ASR_ASM.

+    const signed int v = (signed int)(val >> S)

+    return (unsigned int)(v * -1);

+#endif

 }

 

 /* Field element representation:

@@ -304,7 +325,7 @@ void freduce_degree(limb *output)
   output[0] += output[10];

 }

 

-// Modified for SunCC. See comments for SignExtexnd function.

+// Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

 // #if (-1 & 3) != 3

 // #error "This code only works on a two's complement system"

 // #endif

@@ -317,13 +338,15 @@ inline limb div_by_2_26(const limb v)
   /* High word of v; no shift needed. */

   const word32 highword = (word32) (((word64) v) >> 32);

 

-  // Modified for SunCC. See comments for SignExtexnd function.

+  // Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

   /* Set to all 1s if v was negative; else set to 0s. */

   /* const sword32 sign = ((sword32) highword) >> 31; */

-  const sword32 sign = SignExtend(highword);

+  const word32 sign = SignExtend<31>(highword);

 

   /* Set to 0x3ffffff if v was negative; else set to 0. */

-  const sword32 roundoff = ((word32) sign) >> 6;

+  /* const sword32 roundoff = ((word32) sign) >> 6; */

+  const sword32 roundoff = (sword32)(sign >> 6);

+

   /* Should return v / (1<<26) */

   return (v + roundoff) >> 26;

 }

@@ -336,13 +359,15 @@ inline limb div_by_2_25(const limb v)
   /* High word of v; no shift needed*/

   const word32 highword = (word32) (((word64) v) >> 32);

 

-  // Modified for SunCC. See comments for SignExtexnd function.

+  // Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

   /* Set to all 1s if v was negative; else set to 0s. */

   /* const sword32 sign = ((sword32) highword) >> 31; */

-  const sword32 sign = SignExtend(highword);

+  const word32 sign = SignExtend<31>(highword);

 

   /* Set to 0x1ffffff if v was negative; else set to 0. */

-  const sword32 roundoff = ((word32) sign) >> 7;

+  /* const sword32 roundoff = ((word32) sign) >> 7; */

+  const sword32 roundoff = (sword32)(sign >> 7);

+

   /* Should return v / (1<<25) */

   return (v + roundoff) >> 25;

 }

@@ -517,7 +542,7 @@ void fexpand(limb *output, const byte *input)
 #undef F

 }

 

-// Modified for SunCC. See comments for SignExtexnd function.

+// Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

 // #if (-32 >> 1) != -16

 // #error "This code only works when >> does sign-extension on negative numbers"

 // #endif

@@ -525,7 +550,7 @@ void fexpand(limb *output, const byte *input)
 /* sword32_eq returns 0xffffffff iff a == b and zero otherwise. */

 sword32 sword32_eq(sword32 a, sword32 b)

 {

-  // Modified for SunCC. See comments for SignExtexnd function.

+  // Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

   a = ~(a ^ b);

   a &= a << 16;

   a &= a << 8;

@@ -533,18 +558,18 @@ sword32 sword32_eq(sword32 a, sword32 b)
   a &= a << 2;

   a &= a << 1;

   /* return a >> 31; */

-  return (sword32)SignExtend(a);

+  return (sword32)SignExtend<31>(a);

 }

 

 /* sword32_gte returns 0xffffffff if a >= b and zero otherwise, where a and b are

  * both non-negative. */

 sword32 sword32_gte(sword32 a, sword32 b)

 {

-  // Modified for SunCC. See comments for SignExtexnd function.

+  // Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.

   a -= b;

   /* a >= 0 iff a >= b. */

   /* return ~(a >> 31); */

-  return ~(sword32)SignExtend(a);

+  return ~(sword32)SignExtend<31>(a);

 }

 

 /* Take a fully reduced polynomial form number and contract it into a