void M_log_solve_cubic(M_APM rr, int places, M_APM nn)
{
M_APM tmp0, tmp1, tmp2, tmp3, guess;
int ii, maxp, tolerance, local_precision;
guess = M_get_stack_var();
tmp0 = M_get_stack_var();
tmp1 = M_get_stack_var();
tmp2 = M_get_stack_var();
tmp3 = M_get_stack_var();
M_get_log_guess(guess, nn);
tolerance = -(places + 4);
maxp = places + 16;
local_precision = 18;
/* Use the following iteration to solve for log :
exp(X) - N
X = X - 2 * ------------
n+1 exp(X) + N
this is a cubically convergent algorithm
(each iteration yields 3X more digits)
*/
ii = 0;
while (TRUE)
{
m_apm_exp(tmp1, local_precision, guess);
m_apm_subtract(tmp3, tmp1, nn);
m_apm_add(tmp2, tmp1, nn);
m_apm_divide(tmp1, local_precision, tmp3, tmp2);
m_apm_multiply(tmp0, MM_Two, tmp1);
m_apm_subtract(tmp3, guess, tmp0);
if (ii != 0)
{
if (((3 * tmp0->m_apm_exponent) < tolerance) || (tmp0->m_apm_sign == 0))
break;
}
m_apm_round(guess, local_precision, tmp3);
local_precision *= 3;
if (local_precision > maxp)
local_precision = maxp;
ii = 1;
}
m_apm_round(rr, places, tmp3);
M_restore_stack(5);
}
/*
* find log(N)
*
* if places < 360
* solve with cubically convergent algorithm above
*
* else
*
* let 'X' be 'close' to the solution (we use ~110 decimal places)
*
* let Y = N * exp(-X) - 1
*
* then
*
* log(N) = X + log(1 + Y)
*
* since 'Y' will be small, we can use the efficient log_near_1 algorithm.
*
*/
void M_log_basic_iteration(M_APM rr, int places, M_APM nn)
{
M_APM tmp0, tmp1, tmp2, tmpX;
if (places < 360)
{
M_log_solve_cubic(rr, places, nn);
}
else
{
tmp0 = M_get_stack_var();
tmp1 = M_get_stack_var();
tmp2 = M_get_stack_var();
tmpX = M_get_stack_var();
M_log_solve_cubic(tmpX, 110, nn);
m_apm_negate(tmp0, tmpX);
m_apm_exp(tmp1, (places + 8), tmp0);
m_apm_multiply(tmp2, tmp1, nn);
m_apm_subtract(tmp1, tmp2, MM_One);
M_log_near_1(tmp0, (places - 104), tmp1);
m_apm_add(tmp1, tmpX, tmp0);
m_apm_round(rr, places, tmp1);
M_restore_stack(4);
}
}
/*
* cosh(x) == 0.5 * [ exp(x) + exp(-x) ]
*/
void m_apm_cosh(M_APM rr, int places, M_APM aa)
{
M_APM tmp1, tmp2, tmp3;
int local_precision;
tmp1 = M_get_stack_var();
tmp2 = M_get_stack_var();
tmp3 = M_get_stack_var();
local_precision = places + 4;
m_apm_exp(tmp1, local_precision, aa);
m_apm_reciprocal(tmp2, local_precision, tmp1);
m_apm_add(tmp3, tmp1, tmp2);
m_apm_multiply(tmp1, tmp3, MM_0_5);
m_apm_round(rr, places, tmp1);
M_restore_stack(3);
}
/*
* tanh(x) == [ exp(x) - exp(-x) ] / [ exp(x) + exp(-x) ]
*/
void m_apm_tanh(M_APM rr, int places, M_APM aa)
{
M_APM tmp1, tmp2, tmp3, tmp4;
int local_precision;
tmp1 = M_get_stack_var();
tmp2 = M_get_stack_var();
tmp3 = M_get_stack_var();
tmp4 = M_get_stack_var();
local_precision = places + 4;
m_apm_exp(tmp1, local_precision, aa);
m_apm_reciprocal(tmp2, local_precision, tmp1);
m_apm_subtract(tmp3, tmp1, tmp2);
m_apm_add(tmp4, tmp1, tmp2);
m_apm_divide(tmp1, local_precision, tmp3, tmp4);
m_apm_round(rr, places, tmp1);
M_restore_stack(4);
}
void m_apm_exp_mt(M_APM rr, int places, M_APM aa)
{
m_apm_enter();
m_apm_exp(rr,places,aa);
m_apm_leave();
}
/*
Calculate the POW function by calling EXP :
Y A
X = e where A = Y * log(X)
*/
void m_apm_pow(M_APM rr, int places, M_APM xx, M_APM yy)
{
int iflag, pflag;
char sbuf[64];
M_APM tmp8, tmp9;
/* if yy == 0, return 1 */
if (yy->m_apm_sign == 0)
{
m_apm_copy(rr, MM_One);
return;
}
/* if xx == 0, return 0 */
if (xx->m_apm_sign == 0)
{
M_set_to_zero(rr);
return;
}
if (M_size_flag == 0) /* init locals on first call */
{
M_size_flag = M_get_sizeof_int();
M_last_log_digits = 0;
M_last_xx_input = m_apm_init();
M_last_xx_log = m_apm_init();
}
/*
* if 'yy' is a small enough integer, call the more
* efficient _integer_pow function.
*/
if (m_apm_is_integer(yy))
{
iflag = FALSE;
if (M_size_flag == 2) /* 16 bit compilers */
{
if (yy->m_apm_exponent <= 4)
iflag = TRUE;
}
else /* >= 32 bit compilers */
{
if (yy->m_apm_exponent <= 7)
iflag = TRUE;
}
if (iflag)
{
m_apm_to_integer_string(sbuf, yy);
m_apm_integer_pow(rr, places, xx, atoi(sbuf));
return;
}
}
tmp8 = M_get_stack_var();
tmp9 = M_get_stack_var();
/*
* If parameter 'X' is the same this call as it
* was the previous call, re-use the saved log
* calculation from last time.
*/
pflag = FALSE;
if (M_last_log_digits >= places)
{
if (m_apm_compare(xx, M_last_xx_input) == 0)
pflag = TRUE;
}
if (pflag)
{
m_apm_round(tmp9, (places + 8), M_last_xx_log);
}
else
{
m_apm_log(tmp9, (places + 8), xx);
M_last_log_digits = places + 2;
/* save the 'X' input value and the log calculation */
m_apm_copy(M_last_xx_input, xx);
m_apm_copy(M_last_xx_log, tmp9);
}
m_apm_multiply(tmp8, tmp9, yy);
m_apm_exp(rr, places, tmp8);
M_restore_stack(2); /* restore the 2 locals we used here */
}
