#define UDIV_TIME UMUL_TIME
#endif
-/* FIXME: We should be using invert_limb (or invert_normalized_limb)
- * here (not udiv_qrnnd).
- */
-
-mpi_limb_t
-mpihelp_mod_1(mpi_ptr_t dividend_ptr, mpi_size_t dividend_size,
- mpi_limb_t divisor_limb)
-{
- mpi_size_t i;
- mpi_limb_t n1, n0, r;
- int dummy;
-
- /* Botch: Should this be handled at all? Rely on callers? */
- if (!dividend_size)
- return 0;
-
- /* If multiplication is much faster than division, and the
- * dividend is large, pre-invert the divisor, and use
- * only multiplications in the inner loop.
- *
- * This test should be read:
- * Does it ever help to use udiv_qrnnd_preinv?
- * && Does what we save compensate for the inversion overhead?
- */
- if (UDIV_TIME > (2 * UMUL_TIME + 6)
- && (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME) {
- int normalization_steps;
-
- count_leading_zeros(normalization_steps, divisor_limb);
- if (normalization_steps) {
- mpi_limb_t divisor_limb_inverted;
-
- divisor_limb <<= normalization_steps;
-
- /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
- * result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
- * most significant bit (with weight 2**N) implicit.
- *
- * Special case for DIVISOR_LIMB == 100...000.
- */
- if (!(divisor_limb << 1))
- divisor_limb_inverted = ~(mpi_limb_t) 0;
- else
- udiv_qrnnd(divisor_limb_inverted, dummy,
- -divisor_limb, 0, divisor_limb);
-
- n1 = dividend_ptr[dividend_size - 1];
- r = n1 >> (BITS_PER_MPI_LIMB - normalization_steps);
-
- /* Possible optimization:
- * if (r == 0
- * && divisor_limb > ((n1 << normalization_steps)
- * | (dividend_ptr[dividend_size - 2] >> ...)))
- * ...one division less...
- */
- for (i = dividend_size - 2; i >= 0; i--) {
- n0 = dividend_ptr[i];
- UDIV_QRNND_PREINV(dummy, r, r,
- ((n1 << normalization_steps)
- | (n0 >>
- (BITS_PER_MPI_LIMB -
- normalization_steps))),
- divisor_limb,
- divisor_limb_inverted);
- n1 = n0;
- }
- UDIV_QRNND_PREINV(dummy, r, r,
- n1 << normalization_steps,
- divisor_limb, divisor_limb_inverted);
- return r >> normalization_steps;
- } else {
- mpi_limb_t divisor_limb_inverted;
-
- /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
- * result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
- * most significant bit (with weight 2**N) implicit.
- *
- * Special case for DIVISOR_LIMB == 100...000.
- */
- if (!(divisor_limb << 1))
- divisor_limb_inverted = ~(mpi_limb_t) 0;
- else
- udiv_qrnnd(divisor_limb_inverted, dummy,
- -divisor_limb, 0, divisor_limb);
-
- i = dividend_size - 1;
- r = dividend_ptr[i];
-
- if (r >= divisor_limb)
- r = 0;
- else
- i--;
-
- for (; i >= 0; i--) {
- n0 = dividend_ptr[i];
- UDIV_QRNND_PREINV(dummy, r, r,
- n0, divisor_limb,
- divisor_limb_inverted);
- }
- return r;
- }
- } else {
- if (UDIV_NEEDS_NORMALIZATION) {
- int normalization_steps;
-
- count_leading_zeros(normalization_steps, divisor_limb);
- if (normalization_steps) {
- divisor_limb <<= normalization_steps;
-
- n1 = dividend_ptr[dividend_size - 1];
- r = n1 >> (BITS_PER_MPI_LIMB -
- normalization_steps);
-
- /* Possible optimization:
- * if (r == 0
- * && divisor_limb > ((n1 << normalization_steps)
- * | (dividend_ptr[dividend_size - 2] >> ...)))
- * ...one division less...
- */
- for (i = dividend_size - 2; i >= 0; i--) {
- n0 = dividend_ptr[i];
- udiv_qrnnd(dummy, r, r,
- ((n1 << normalization_steps)
- | (n0 >>
- (BITS_PER_MPI_LIMB -
- normalization_steps))),
- divisor_limb);
- n1 = n0;
- }
- udiv_qrnnd(dummy, r, r,
- n1 << normalization_steps,
- divisor_limb);
- return r >> normalization_steps;
- }
- }
- /* No normalization needed, either because udiv_qrnnd doesn't require
- * it, or because DIVISOR_LIMB is already normalized. */
- i = dividend_size - 1;
- r = dividend_ptr[i];
-
- if (r >= divisor_limb)
- r = 0;
- else
- i--;
-
- for (; i >= 0; i--) {
- n0 = dividend_ptr[i];
- udiv_qrnnd(dummy, r, r, n0, divisor_limb);
- }
- return r;
- }
-}
-
/* Divide num (NP/NSIZE) by den (DP/DSIZE) and write
* the NSIZE-DSIZE least significant quotient limbs at QP
* and the DSIZE long remainder at NP. If QEXTRA_LIMBS is
return most_significant_q_limb;
}
-
-/****************
- * Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB.
- * Write DIVIDEND_SIZE limbs of quotient at QUOT_PTR.
- * Return the single-limb remainder.
- * There are no constraints on the value of the divisor.
- *
- * QUOT_PTR and DIVIDEND_PTR might point to the same limb.
- */
-
-mpi_limb_t
-mpihelp_divmod_1(mpi_ptr_t quot_ptr,
- mpi_ptr_t dividend_ptr, mpi_size_t dividend_size,
- mpi_limb_t divisor_limb)
-{
- mpi_size_t i;
- mpi_limb_t n1, n0, r;
- int dummy;
-
- if (!dividend_size)
- return 0;
-
- /* If multiplication is much faster than division, and the
- * dividend is large, pre-invert the divisor, and use
- * only multiplications in the inner loop.
- *
- * This test should be read:
- * Does it ever help to use udiv_qrnnd_preinv?
- * && Does what we save compensate for the inversion overhead?
- */
- if (UDIV_TIME > (2 * UMUL_TIME + 6)
- && (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME) {
- int normalization_steps;
-
- count_leading_zeros(normalization_steps, divisor_limb);
- if (normalization_steps) {
- mpi_limb_t divisor_limb_inverted;
-
- divisor_limb <<= normalization_steps;
-
- /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
- * result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
- * most significant bit (with weight 2**N) implicit.
- */
- /* Special case for DIVISOR_LIMB == 100...000. */
- if (!(divisor_limb << 1))
- divisor_limb_inverted = ~(mpi_limb_t) 0;
- else
- udiv_qrnnd(divisor_limb_inverted, dummy,
- -divisor_limb, 0, divisor_limb);
-
- n1 = dividend_ptr[dividend_size - 1];
- r = n1 >> (BITS_PER_MPI_LIMB - normalization_steps);
-
- /* Possible optimization:
- * if (r == 0
- * && divisor_limb > ((n1 << normalization_steps)
- * | (dividend_ptr[dividend_size - 2] >> ...)))
- * ...one division less...
- */
- for (i = dividend_size - 2; i >= 0; i--) {
- n0 = dividend_ptr[i];
- UDIV_QRNND_PREINV(quot_ptr[i + 1], r, r,
- ((n1 << normalization_steps)
- | (n0 >>
- (BITS_PER_MPI_LIMB -
- normalization_steps))),
- divisor_limb,
- divisor_limb_inverted);
- n1 = n0;
- }
- UDIV_QRNND_PREINV(quot_ptr[0], r, r,
- n1 << normalization_steps,
- divisor_limb, divisor_limb_inverted);
- return r >> normalization_steps;
- } else {
- mpi_limb_t divisor_limb_inverted;
-
- /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
- * result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
- * most significant bit (with weight 2**N) implicit.
- */
- /* Special case for DIVISOR_LIMB == 100...000. */
- if (!(divisor_limb << 1))
- divisor_limb_inverted = ~(mpi_limb_t) 0;
- else
- udiv_qrnnd(divisor_limb_inverted, dummy,
- -divisor_limb, 0, divisor_limb);
-
- i = dividend_size - 1;
- r = dividend_ptr[i];
-
- if (r >= divisor_limb)
- r = 0;
- else
- quot_ptr[i--] = 0;
-
- for (; i >= 0; i--) {
- n0 = dividend_ptr[i];
- UDIV_QRNND_PREINV(quot_ptr[i], r, r,
- n0, divisor_limb,
- divisor_limb_inverted);
- }
- return r;
- }
- } else {
- if (UDIV_NEEDS_NORMALIZATION) {
- int normalization_steps;
-
- count_leading_zeros(normalization_steps, divisor_limb);
- if (normalization_steps) {
- divisor_limb <<= normalization_steps;
-
- n1 = dividend_ptr[dividend_size - 1];
- r = n1 >> (BITS_PER_MPI_LIMB -
- normalization_steps);
-
- /* Possible optimization:
- * if (r == 0
- * && divisor_limb > ((n1 << normalization_steps)
- * | (dividend_ptr[dividend_size - 2] >> ...)))
- * ...one division less...
- */
- for (i = dividend_size - 2; i >= 0; i--) {
- n0 = dividend_ptr[i];
- udiv_qrnnd(quot_ptr[i + 1], r, r,
- ((n1 << normalization_steps)
- | (n0 >>
- (BITS_PER_MPI_LIMB -
- normalization_steps))),
- divisor_limb);
- n1 = n0;
- }
- udiv_qrnnd(quot_ptr[0], r, r,
- n1 << normalization_steps,
- divisor_limb);
- return r >> normalization_steps;
- }
- }
- /* No normalization needed, either because udiv_qrnnd doesn't require
- * it, or because DIVISOR_LIMB is already normalized. */
- i = dividend_size - 1;
- r = dividend_ptr[i];
-
- if (r >= divisor_limb)
- r = 0;
- else
- quot_ptr[i--] = 0;
-
- for (; i >= 0; i--) {
- n0 = dividend_ptr[i];
- udiv_qrnnd(quot_ptr[i], r, r, n0, divisor_limb);
- }
- return r;
- }
-}
projects / linux.git / blobdiff