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Cleanup donna_32.cpp arithmetic shift

pull/765/head
Jeffrey Walton 2018-12-12 22:52:15 -05:00
parent a09d4024b7
commit 459035fcaa
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GPG Key ID: B36AB348921B1838
1 changed files with 60 additions and 35 deletions
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donna_32.cpp
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@ -56,10 +56,9 @@
#include "stdcpp.h" #include "stdcpp.h"
#include "cpu.h" #include "cpu.h"
// This macro is not in a header like config.h because // This macro is not in a header like config.h because we don't want it
// we don't want it exposed to user code. We also need // exposed to user code. We also need a standard header like <stdint.h>
// a standard header like <stdint.h> or <stdef.h>. // or <stdef.h>. Langley uses uint128_t in the 64-bit code paths so
// Langley uses uint128_t in the 64-bit code paths so
// we further restrict 64-bit code. // we further restrict 64-bit code.
#if (UINTPTR_MAX == 0xffffffff) || !defined(CRYPTOPP_WORD128_AVAILABLE) #if (UINTPTR_MAX == 0xffffffff) || !defined(CRYPTOPP_WORD128_AVAILABLE)
# define CRYPTOPP_32BIT 1 # define CRYPTOPP_32BIT 1
@ -67,6 +66,16 @@
# define CRYPTOPP_64BIT 1 # define CRYPTOPP_64BIT 1
#endif #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 // Squash MS LNK4221 and libtool warnings
extern const char DONNA32_FNAME[] = __FILE__; extern const char DONNA32_FNAME[] = __FILE__;
@ -84,41 +93,53 @@ using CryptoPP::sword64;
typedef sword64 limb; typedef sword64 limb;
// Added by JW for SunCC. Avoid the bit twiddling hacks. // Added by JW for SunCC. Avoid the bit twiddling hacks.
template <unsigned int S>
inline int SignExtend(int val) inline int SignExtend(int val)
{ {
#if (__GNUC__ >= 3) || (__SUNPRO_CC >= 0x5100) #if defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_X86)
# if CRYPTOPP_BOOL_X86
__asm__ __asm__
( (
"sar $31, %0 \n" "sar %1, %0 \n"
: "+g" (val) : : "cc" : "+g" (val) : "I" (S) : "cc"
); );
return val; return val;
# endif #elif defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_ARM32)
// TODO: ARM __asm__
#endif (
"asr %0, %0, %1 \n"
: "+r" (val) : "I" (S) :
);
return val;
#else
// GCC and SunCC compile down to a shift and neg. // 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) inline unsigned int SignExtend(unsigned int val)
{ {
#if (__GNUC__ >= 3) || (__SUNPRO_CC >= 0x5100) #if defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_X86)
# if CRYPTOPP_BOOL_X86
__asm__ __asm__
( (
"sar $31, %0 \n" "sar %1, %0 \n"
: "+g" (val) : : "cc" : "+g" (val) : "I" (S) : "cc"
); );
return val; return val;
# endif #elif defined(CRYPTOPP_ASR_ASM) && (CRYPTOPP_BOOL_ARM32)
// TODO: ARM __asm__
#endif (
"asr %0, %0, %1 \n"
: "+r" (val) : "I" (S) :
);
return val;
#else
// GCC and SunCC compile down to a shift and neg. // 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: /* Field element representation:
@ -304,7 +325,7 @@ void freduce_degree(limb *output)
output[0] += output[10]; 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 // #if (-1 & 3) != 3
// #error "This code only works on a two's complement system" // #error "This code only works on a two's complement system"
// #endif // #endif
@ -317,13 +338,15 @@ inline limb div_by_2_26(const limb v)
/* High word of v; no shift needed. */ /* High word of v; no shift needed. */
const word32 highword = (word32) (((word64) v) >> 32); 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. */ /* Set to all 1s if v was negative; else set to 0s. */
/* const sword32 sign = ((sword32) highword) >> 31; */ /* 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. */ /* 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) */ /* Should return v / (1<<26) */
return (v + roundoff) >> 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*/ /* High word of v; no shift needed*/
const word32 highword = (word32) (((word64) v) >> 32); 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. */ /* Set to all 1s if v was negative; else set to 0s. */
/* const sword32 sign = ((sword32) highword) >> 31; */ /* 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. */ /* 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) */ /* Should return v / (1<<25) */
return (v + roundoff) >> 25; return (v + roundoff) >> 25;
} }
@ -517,7 +542,7 @@ void fexpand(limb *output, const byte *input)
#undef F #undef F
} }
// Modified for SunCC. See comments for SignExtexnd function. // Modified for SunCC. See comments for CRYPTOPP_ASR_ASM.
// #if (-32 >> 1) != -16 // #if (-32 >> 1) != -16
// #error "This code only works when >> does sign-extension on negative numbers" // #error "This code only works when >> does sign-extension on negative numbers"
// #endif // #endif
@ -525,7 +550,7 @@ void fexpand(limb *output, const byte *input)
/* sword32_eq returns 0xffffffff iff a == b and zero otherwise. */ /* sword32_eq returns 0xffffffff iff a == b and zero otherwise. */
sword32 sword32_eq(sword32 a, sword32 b) 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 ^ b);
a &= a << 16; a &= a << 16;
a &= a << 8; a &= a << 8;
@ -533,18 +558,18 @@ sword32 sword32_eq(sword32 a, sword32 b)
a &= a << 2; a &= a << 2;
a &= a << 1; a &= a << 1;
/* return a >> 31; */ /* 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 /* sword32_gte returns 0xffffffff if a >= b and zero otherwise, where a and b are
* both non-negative. */ * both non-negative. */
sword32 sword32_gte(sword32 a, sword32 b) 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 -= b;
/* a >= 0 iff a >= b. */ /* a >= 0 iff a >= b. */
/* return ~(a >> 31); */ /* return ~(a >> 31); */
return ~(sword32)SignExtend(a); return ~(sword32)SignExtend<31>(a);
} }
/* Take a fully reduced polynomial form number and contract it into a /* Take a fully reduced polynomial form number and contract it into a