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/*										*/
/*			Simple Operations on Big Numbers     			*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
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//** Introduction
// The simulator code uses the canonical form whenever possible in order to make
// the code in Part 3 more accessible. The canonical data formats are simple and
// not well suited for complex big number computations. When operating on big
// numbers, the data format is changed for easier manipulation. The format is native
// words in little-endian format. As the magnitude of the number decreases, the
// length of the array containing the number decreases but the starting address
// doesn't change.
//
// The functions in this file perform simple operations on these big numbers. Only
// the more complex operations are passed to the underlying support library.
// Although the support library would have most of these functions, the interface
// code to convert the format for the values is greater than the size of the
// code to implement the functions here. So, rather than incur the overhead of
// conversion, they are done here.
//
// If an implementer would prefer, the underlying library can be used simply by
// making code substitutions here.
//
// NOTE: There is an intention to continue to augment these functions so that there
// would be no need to use an external big number library.
//
// Many of these functions have no error returns and will always return TRUE. This
// is to allow them to be used in "guarded" sequences. That is:
//    OK = OK || BnSomething(s);
// where the BnSomething() function should not be called if OK isn't true.

//** Includes
#include "TpmBigNum.h"
extern BOOL g_inFailureMode;  // can't use global.h because we can't use tpm.h

// A constant value of zero as a stand in for NULL bigNum values
const bignum_t BnConstZero = {1, 0, {0}};

//** Functions

//*** AddSame()
// Adds two values that are the same size. This function allows 'result' to be
// the same as either of the addends. This is a nice function to put into assembly
// because handling the carry for multi-precision stuff is not as easy in C
// (unless there is a REALLY smart compiler). It would be nice if there were idioms
// in a language that a compiler could recognize what is going on and optimize
// loops like this.
//  Return Type: int
//      0           no carry out
//      1           carry out
static BOOL AddSame(crypt_uword_t*       result,
		    const crypt_uword_t* op1,
		    const crypt_uword_t* op2,
		    int                  count)
{
    int carry = 0;
    int i;

    for(i = 0; i < count; i++)
	{
	    crypt_uword_t a   = op1[i];
	    crypt_uword_t sum = a + op2[i];
	    result[i]         = sum + carry;
	    // generate a carry if the sum is less than either of the inputs
	    // propagate a carry if there was a carry and the sum + carry is zero
	    // do this using bit operations rather than logical operations so that
	    // the time is about the same.
	    //             propagate term      | generate term
	    carry = ((result[i] == 0) & carry) | (sum < a);
	}
    return carry;
}

//*** CarryProp()
// Propagate a carry
static int CarryProp(
		     crypt_uword_t* result, const crypt_uword_t* op, int count, int carry)
{
    for(; count; count--)
	carry = ((*result++ = *op++ + carry) == 0) & carry;
    return carry;
}

static void CarryResolve(bigNum result, int stop, int carry)
{
    if(carry)
	{
	    pAssert((unsigned)stop < result->allocated);
	    result->d[stop++] = 1;
	}
    BnSetTop(result, stop);
}

//*** BnAdd()
// This function adds two bigNum values. This function always returns TRUE.
LIB_EXPORT BOOL BnAdd(bigNum result, bigConst op1, bigConst op2)
{
    crypt_uword_t   stop;
    int             carry;
    const bignum_t* n1 = op1;
    const bignum_t* n2 = op2;

    //
    if(n2->size > n1->size)
	{
	    n1 = op2;
	    n2 = op1;
	}
    pAssert(result->allocated >= n1->size);
    stop  = MIN(n1->size, n2->allocated);
    carry = (int)AddSame(result->d, n1->d, n2->d, (int)stop);
    if(n1->size > stop)
	carry =
	    CarryProp(&result->d[stop], &n1->d[stop], (int)(n1->size - stop), carry);
    CarryResolve(result, (int)n1->size, carry);
    return TRUE;
}

//*** BnAddWord()
// This function adds a word value to a bigNum. This function always returns TRUE.
LIB_EXPORT BOOL BnAddWord(bigNum result, bigConst op, crypt_uword_t word)
{
    int carry;
    //
    carry = (result->d[0] = op->d[0] + word) < word;
    carry = CarryProp(&result->d[1], &op->d[1], (int)(op->size - 1), carry);
    CarryResolve(result, (int)op->size, carry);
    return TRUE;
}

//*** SubSame()
// This function subtracts two values that have the same size.
static int SubSame(crypt_uword_t*       result,
		   const crypt_uword_t* op1,
		   const crypt_uword_t* op2,
		   int                  count)
{
    int borrow = 0;
    int i;
    for(i = 0; i < count; i++)
	{
	    crypt_uword_t a    = op1[i];
	    crypt_uword_t diff = a - op2[i];
	    result[i]          = diff - borrow;
	    //       generate   |      propagate
	    borrow = (diff > a) | ((diff == 0) & borrow);
	}
    return borrow;
}

//*** BorrowProp()
// This propagates a borrow. If borrow is true when the end
// of the array is reached, then it means that op2 was larger than
// op1 and we don't handle that case so an assert is generated.
// This design choice was made because our only bigNum computations
// are on large positive numbers (primes) or on fields.
// Propagate a borrow.
static int BorrowProp(
		      crypt_uword_t* result, const crypt_uword_t* op, int size, int borrow)
{
    for(; size > 0; size--)
	borrow = ((*result++ = *op++ - borrow) == MAX_CRYPT_UWORD) && borrow;
    return borrow;
}

//*** BnSub()
// This function does subtraction of two bigNum values and returns result = op1 - op2
// when op1 is greater than op2. If op2 is greater than op1, then a fault is
// generated. This function always returns TRUE.
LIB_EXPORT BOOL BnSub(bigNum result, bigConst op1, bigConst op2)
{
    int borrow;
    int stop = (int)MIN(op1->size, op2->allocated);
    //
    // Make sure that op2 is not obviously larger than op1
    pAssert(op1->size >= op2->size);
    borrow = SubSame(result->d, op1->d, op2->d, stop);
    if(op1->size > (crypt_uword_t)stop)
	borrow = BorrowProp(
			    &result->d[stop], &op1->d[stop], (int)(op1->size - stop), borrow);
    pAssert(!borrow);
    BnSetTop(result, op1->size);
    return TRUE;
}

//*** BnSubWord()
// This function subtracts a word value from a bigNum. This function always
// returns TRUE.
LIB_EXPORT BOOL BnSubWord(bigNum result, bigConst op, crypt_uword_t word)
{
    int borrow;
    //
    pAssert(op->size > 1 || word <= op->d[0]);
    borrow       = word > op->d[0];
    result->d[0] = op->d[0] - word;
    borrow       = BorrowProp(&result->d[1], &op->d[1], (int)(op->size - 1), borrow);
    pAssert(!borrow);
    BnSetTop(result, op->size);
    return TRUE;
}

//*** BnUnsignedCmp()
// This function performs a comparison of op1 to op2. The compare is approximately
// constant time if the size of the values used in the compare is consistent
// across calls (from the same line in the calling code).
//  Return Type: int
//      < 0             op1 is less than op2
//      0               op1 is equal to op2
//      > 0             op1 is greater than op2
LIB_EXPORT int BnUnsignedCmp(bigConst op1, bigConst op2)
{
    int retVal;
    int diff;
    int i;
    //
    pAssert((op1 != NULL) && (op2 != NULL));
    retVal = (int)(op1->size - op2->size);
    if(retVal == 0)
	{
	    for(i = (int)(op1->size - 1); i >= 0; i--)
		{
		    diff   = (op1->d[i] < op2->d[i]) ? -1 : (op1->d[i] != op2->d[i]);
		    retVal = retVal == 0 ? diff : retVal;
		}
	}
    else
	retVal = (retVal < 0) ? -1 : 1;
    return retVal;
}

//*** BnUnsignedCmpWord()
// Compare a bigNum to a crypt_uword_t.
//  Return Type: int
//      -1              op1 is less that word
//      0               op1 is equal to word
//      1               op1 is greater than word
LIB_EXPORT int BnUnsignedCmpWord(bigConst op1, crypt_uword_t word)
{
    if(op1->size > 1)
	return 1;
    else if(op1->size == 1)
	return (op1->d[0] < word) ? -1 : (op1->d[0] > word);
    else  // op1 is zero
	// equal if word is zero
	return (word == 0) ? 0 : -1;
}

//*** BnModWord()
// This function does modular division of a big number when the modulus is a
// word value.
LIB_EXPORT crypt_word_t BnModWord(bigConst numerator, crypt_word_t modulus)
{
    BN_MAX(remainder);
    BN_VAR(mod, RADIX_BITS);
    //
    mod->d[0] = modulus;
    mod->size = (modulus != 0);
    BnDiv(NULL, remainder, numerator, mod);
    return remainder->d[0];
}

//*** Msb()
// This function returns the bit number of the most significant bit of a
// crypt_uword_t. The number for the least significant bit of any bigNum value is 0.
// The maximum return value is RADIX_BITS - 1,
//  Return Type: int
//      -1              the word was zero
//      n               the bit number of the most significant bit in the word
static int Msb(crypt_uword_t word)
{
    int retVal = -1;
    //
#if RADIX_BITS == 64
    if(word & 0xffffffff00000000)
	{
	    retVal += 32;
	    word >>= 32;
	}
#endif
    if(word & 0xffff0000)
	{
	    retVal += 16;
	    word >>= 16;
	}
    if(word & 0x0000ff00)
	{
	    retVal += 8;
	    word >>= 8;
	}
    if(word & 0x000000f0)
	{
	    retVal += 4;
	    word >>= 4;
	}
    if(word & 0x0000000c)
	{
	    retVal += 2;
	    word >>= 2;
	}
    if(word & 0x00000002)
	{
	    retVal += 1;
	    word >>= 1;
	}
    return retVal + (int)word;
}

//*** BnMsb()
// This function returns the number of the MSb of a bigNum value.
//  Return Type: int
//      -1              the word was zero or 'bn' was NULL
//      n               the bit number of the most significant bit in the word
LIB_EXPORT int BnMsb(bigConst bn)
{
    // If the value is NULL, or the size is zero then treat as zero and return -1
    if(bn != NULL && bn->size > 0)
	{
	    int retVal = Msb(bn->d[bn->size - 1]);
	    retVal += (int)(bn->size - 1) * RADIX_BITS;
	    return retVal;
	}
    else
	return -1;
}

//*** BnSizeInBits()
// This function returns the number of bits required to hold a number. It is one
// greater than the Msb.
//
LIB_EXPORT unsigned BnSizeInBits(bigConst n)
{
    int bits = BnMsb(n) + 1;
    //
    return bits < 0 ? 0 : (unsigned)bits;
}

//*** BnSetWord()
// Change the value of a bignum_t to a word value.
LIB_EXPORT bigNum BnSetWord(bigNum n, crypt_uword_t w)
{
    if(n != NULL)
	{
	    pAssert(n->allocated > 1);
	    n->d[0] = w;
	    BnSetTop(n, (w != 0) ? 1 : 0);
	}
    return n;
}

//*** BnSetBit()
// This function will SET a bit in a bigNum. Bit 0 is the least-significant bit in
// the 0th digit_t.  The function will return FALSE if the bitNum is invalid, else TRUE.
LIB_EXPORT BOOL BnSetBit(bigNum       bn,     // IN/OUT: big number to modify
			 unsigned int bitNum  // IN: Bit number to SET
			 )
{
    crypt_uword_t offset = bitNum / RADIX_BITS;
    if(bitNum > bn->allocated * RADIX_BITS)
	{
	    // out of range
	    return FALSE;
	}
    // Grow the number if necessary to set the bit.
    while(bn->size <= offset)
	bn->d[bn->size++] = 0;
    bn->d[offset] |= ((crypt_uword_t)1 << RADIX_MOD(bitNum));
    return TRUE;
}

//*** BnTestBit()
// This function is used to check to see if a bit is SET in a bignum_t. The 0th bit
// is the LSb of d[0].
//  Return Type: BOOL
//      TRUE(1)         the bit is set
//      FALSE(0)        the bit is not set or the number is out of range
LIB_EXPORT BOOL BnTestBit(bigNum       bn,     // IN: number to check
			  unsigned int bitNum  // IN: bit to test
			  )
{
    crypt_uword_t offset = RADIX_DIV(bitNum);
    //
    if(bn->size > offset)
	return ((bn->d[offset] & (((crypt_uword_t)1) << RADIX_MOD(bitNum))) != 0);
    else
	return FALSE;
}

//***BnMaskBits()
// This function is used to mask off high order bits of a big number.
// The returned value will have no more than 'maskBit' bits
// set.
// Note: There is a requirement that unused words of a bignum_t are set to zero.
//  Return Type: BOOL
//      TRUE(1)         result masked
//      FALSE(0)        the input was not as large as the mask
LIB_EXPORT BOOL BnMaskBits(bigNum        bn,      // IN/OUT: number to mask
			   crypt_uword_t maskBit  // IN: the bit number for the mask.
			   )
{
    crypt_uword_t finalSize;
    BOOL          retVal;

    finalSize = BITS_TO_CRYPT_WORDS(maskBit);
    retVal    = (finalSize <= bn->allocated);
    if(retVal && (finalSize > 0))
	{
	    crypt_uword_t mask;
	    mask = ~((crypt_uword_t)0) >> RADIX_MOD(maskBit);
	    bn->d[finalSize - 1] &= mask;
	}
    BnSetTop(bn, finalSize);
    return retVal;
}

//*** BnShiftRight()
// This function will shift a bigNum to the right by the shiftAmount.
// This function always returns TRUE.
LIB_EXPORT BOOL BnShiftRight(bigNum result, bigConst toShift, uint32_t shiftAmount)
{
    uint32_t      offset = (shiftAmount >> RADIX_LOG2);
    uint32_t      i;
    uint32_t      shiftIn;
    crypt_uword_t finalSize;
    //
    shiftAmount = shiftAmount & RADIX_MASK;
    shiftIn     = RADIX_BITS - shiftAmount;

    // The end size is toShift->size - offset less one additional
    // word if the shiftAmount would make the upper word == 0
    if(toShift->size > offset)
	{
	    finalSize = toShift->size - offset;
	    finalSize -= (toShift->d[toShift->size - 1] >> shiftAmount) == 0 ? 1 : 0;
	}
    else
	finalSize = 0;

    pAssert(finalSize <= result->allocated);
    if(finalSize != 0)
	{
	    for(i = 0; i < finalSize; i++)
		{
		    result->d[i] = (toShift->d[i + offset] >> shiftAmount)
				   | (toShift->d[i + offset + 1] << shiftIn);
		}
	    if(offset == 0)
		result->d[i] = toShift->d[i] >> shiftAmount;
	}
    BnSetTop(result, finalSize);
    return TRUE;
}

//*** BnIsPointOnCurve()
// This function checks if a point is on the curve.
BOOL BnIsPointOnCurve(pointConst Q, const TPMBN_ECC_CURVE_CONSTANTS* C)
{
    BN_VAR(right, (MAX_ECC_KEY_BITS * 3));
    BN_VAR(left, (MAX_ECC_KEY_BITS * 2));
    bigConst prime = BnCurveGetPrime(C);
    //
    // Show that point is on the curve y^2 = x^3 + ax + b;
    // Or y^2 = x(x^2 + a) + b
    // y^2
    BnMult(left, Q->y, Q->y);

    BnMod(left, prime);
    // x^2
    BnMult(right, Q->x, Q->x);

    // x^2 + a
    BnAdd(right, right, BnCurveGet_a(C));

    //    ExtMath_Mod(right, CurveGetPrime(C));
    // x(x^2 + a)
    BnMult(right, right, Q->x);

    // x(x^2 + a) + b
    BnAdd(right, right, BnCurveGet_b(C));

    BnMod(right, prime);
    if(BnUnsignedCmp(left, right) == 0)
	return TRUE;
    else
	return FALSE;
}