cln_mirror/src/integer/conv/cl_I_from_digits.cc

// digits_to_I().

// General includes.
#include "base/cl_sysdep.h"

// Specification.
#include "integer/cl_I.h"


// Implementation.

#include "base/digitseq/cl_DS.h"
#include "integer/conv/cl_I_cached_power.h"

namespace cln {

static const cl_I digits_to_I_base2 (const char * MSBptr, uintC len, uintD base)
{
	// base is a power of two: write the digits from least significant
	// to most significant into the result NUDS. Result needs
	// 1+ceiling(len*log(base)/(intDsize*log(2))) or some more digits.
	CL_ALLOCA_STACK;
	var uintD* erg_MSDptr;
	var uintC erg_len;
	var uintD* erg_LSDptr;
	var int b = (base==2 ? 1 : base==4 ? 2 : base==8 ? 3 : base==16 ? 4 : /*base==32*/ 5);
	num_stack_alloc(1+(len*b)/intDsize,,erg_LSDptr=);
	erg_MSDptr = erg_LSDptr; erg_len = 0;
	var uintD d = 0;  // resulting digit
	var int ch_where = 0;  // position of ch inside d
	var uintC min_len = 0;  // first non-zero digit
	while (min_len < len && *(const uintB *)(MSBptr+min_len) == '0') {
	    ++min_len;
	}
	while (len > min_len) {
		var uintB ch = *(const uintB *)(MSBptr+len-1); // next character
		if (ch!='.') { // skip decimal point
			// Compute value of ch ('0'-'9','A'-'Z','a'-'z'):
			ch = ch - '0';
			if (ch > '9'-'0') { // not a digit?
				ch = ch+'0'-'A'+10;
				if (ch > 'Z'-'A'+10) {// not an uppercase letter?
					ch = ch+'A'-'a'; // must be lowercase!
				}
			}
			d = d | (uintD)ch<<ch_where;
			ch_where = ch_where+b;
			if (ch_where >= intDsize) {
			    // d is ready to be written into the NUDS:
			    lsprefnext(erg_MSDptr) = d;
			    ch_where = ch_where-intDsize;
			    d = (uintD)ch >> b-ch_where;  // carry
			    erg_len++;
			}
		}
		len--;
	}
	if (d != 0) {  // is there anything left over?
		lsprefnext(erg_MSDptr) = d;
		++erg_len;
	}
	return NUDS_to_I(erg_MSDptr,erg_len);
}

static const cl_I digits_to_I_baseN (const char * MSBptr, uintC len, uintD base)
{
	// base is not a power of two: Add digits one by one. Result needs
	// 1+ceiling(len*log(base)/(intDsize*log(2))) or some more digits.
	CL_ALLOCA_STACK;
	var uintD* erg_MSDptr;
	var uintC erg_len;
	var uintD* erg_LSDptr;
	var uintC need = 1+floor(len,intDsize*256); // > len/(intDsize*256) >=0
	switch (base) { // multiply need with ceiling(256*log(base)/log(2)):
		case 2: need = 256*need; break;
		case 3: need = 406*need; break;
		case 4: need = 512*need; break;
		case 5: need = 595*need; break;
		case 6: need = 662*need; break;
		case 7: need = 719*need; break;
		case 8: need = 768*need; break;
		case 9: need = 812*need; break;
		case 10: need = 851*need; break;
		case 11: need = 886*need; break;
		case 12: need = 918*need; break;
		case 13: need = 948*need; break;
		case 14: need = 975*need; break;
		case 15: need = 1001*need; break;
		case 16: need = 1024*need; break;
		case 17: need = 1047*need; break;
		case 18: need = 1068*need; break;
		case 19: need = 1088*need; break;
		case 20: need = 1107*need; break;
		case 21: need = 1125*need; break;
		case 22: need = 1142*need; break;
		case 23: need = 1159*need; break;
		case 24: need = 1174*need; break;
		case 25: need = 1189*need; break;
		case 26: need = 1204*need; break;
		case 27: need = 1218*need; break;
		case 28: need = 1231*need; break;
		case 29: need = 1244*need; break;
		case 30: need = 1257*need; break;
		case 31: need = 1269*need; break;
		case 32: need = 1280*need; break;
		case 33: need = 1292*need; break;
		case 34: need = 1303*need; break;
		case 35: need = 1314*need; break;
		case 36: need = 1324*need; break;
		default: NOTREACHED
	}
	// Now we have need >= len*log(base)/(intDsize*log(2)).
	need += 1;
	// Add digits one by one:
	num_stack_alloc(need,,erg_LSDptr=);
	// erg_MSDptr/erg_len/erg_LSDptr is a NUDS, erg_len < need.
	erg_MSDptr = erg_LSDptr; erg_len = 0;
	while (len > 0) {
		var uintD newdigit = 0;
		var uintC chx = 0;
		var uintD factor = 1;
		while (chx < power_table[base-2].k && len > 0) {
			var uintB ch = *(const uintB *)MSBptr; MSBptr++; // next character
			// Compute value of ('0'-'9','A'-'Z','a'-'z'):
			ch = ch-'0';
			if (ch > '9'-'0') { // not a digit?
				ch = ch+'0'-'A'+10;
				if (ch > 'Z'-'A'+10) {// not an uppercase letter?
					ch = ch+'A'-'a';  // must be lowercase!
				}
			}
			factor = factor*base;
			newdigit = base*newdigit+ch;
			chx++;
			len--;
		}
		var uintD carry = mulusmall_loop_lsp(factor,erg_LSDptr,erg_len,newdigit);
		if (carry!=0) {
			// need to extend NUDS:
			lsprefnext(erg_MSDptr) = carry;
			erg_len++;
		}
	}
	return NUDS_to_I(erg_MSDptr,erg_len);
}

static const cl_I digits_to_I_divconq (const char * MSBptr, uintC len, uintD base)
{
	// This is quite insensitive to the breakeven point.
	// On a 1GHz Athlon I get approximately:
	//   base  3: breakeven around 25000
	//   base 10: breakeven around  8000
	//   base 36: breakeven around  2000
	if (len>80000/base) {
		// Divide-and-conquer:
		// Find largest i such that B = base^(k*2^i) satisfies B <= X.
		var const cached_power_table_entry * p;
		var uintC len_B = power_table[base-2].k;
		for (uintC i = 0; ; i++) {
			p = cached_power(base, i);
			if (2*len_B >= len)
				break;
			len_B = len_B*2;
		}
			return digits_to_I_divconq(MSBptr,len-len_B,base) * p->base_pow
			     + digits_to_I_divconq(MSBptr+len-len_B,len_B,base);
	} else {
		return digits_to_I_baseN(MSBptr, len, base);
	}
}

const cl_I digits_to_I (const char * MSBptr, uintC len, uintD base)
{
	if ((base & (base-1)) == 0) {
		return digits_to_I_base2(MSBptr, len, base);
	} else {
		// digits_to_I_divconq cannot handle decimal points, so remove it here
		CL_ALLOCA_STACK;
		const uintD * digits_copy;
		num_stack_alloc(len,,digits_copy=);
		char * copy_ptr = (char *)digits_copy;
		uintC n = 0;
		for (uintC i = 0; i < len; ++i) {
			const char ch = MSBptr[i];
			if (ch != '.') { // skip decimal point
				copy_ptr[n] = ch;
				n++;
			}
		}
		return digits_to_I_divconq((const char*)digits_copy, n, base);
	}
}

}  // namespace cln