* src/integer/conv/cl_I_from_digits.cc (digits_to_I): Speedup when

the base is a power of two.

ChangeLog

@@ -1,3 +1,8 @@
+2004-10-12  Richard B. Kreckel  <kreckel@ginac.de>
+
+	* src/integer/conv/cl_I_from_digits.cc (digits_to_I): Speedup when
+	the base is a power of two.
+
 2004-10-05  Richard B. Kreckel  <kreckel@ginac.de>
 
 	* src/integer/conv/cl_I_to_digits.cc (I_to_digits): Fix bug in base 32.

src/integer/conv/cl_I_from_digits.cc

@@ -19,17 +19,54 @@ const cl_I digits_to_I (const char * MSBptr, uintL len, uintD base)
       var uintD* erg_MSDptr;
       var uintC erg_len;
       var uintD* erg_LSDptr;
+      if ((base & (base-1)) == 0) {
+        // Fast path for powers of two: write the digits from least
+        // significant to most significant into the result NUDS.
+        var int b = (base==2 ? 1 : base==4 ? 2 : base==8 ? 3 : base==16 ? 4 : /*base==32*/ 5);
+        num_stack_alloc(1+(len*b-1)/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
+        while (len > 0)
+          { 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;
+        }
+      } else {
+        // Slow path: Add digits one by one for non-powers of two.
         // Platz fürs Ergebnis:
-      // 1+ceiling(len*log(base)/(intDsize*log(2))) oder etwas mehr Digits
+        // 1+ceiling(len*log(base)/(intDsize*log(2))) or some more digits
         var uintL need = 1+floor(len,intDsize*256); // > len/(intDsize*256) >=0
-      switch (base) // need mit ceiling(256*log(base)/log(2)) multiplizieren:
-        { case 2: need = 256*need; break;
+        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 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 8: need = 768*need; break;
             case 9: need = 812*need; break;
             case 10: need = 851*need; break;
             case 11: need = 886*need; break;
@@ -37,7 +74,7 @@ const cl_I digits_to_I (const char * MSBptr, uintL len, uintD base)
             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 16: need = 1024*need; break;
             case 17: need = 1047*need; break;
             case 18: need = 1068*need; break;
             case 19: need = 1088*need; break;
@@ -53,37 +90,38 @@ const cl_I digits_to_I (const char * MSBptr, uintL len, uintD base)
             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 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
           }
-      // Nun gilt need >= len*log(base)/(intDsize*log(2)).
+        // 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_LSDptr; erg_len = 0;
-      // Ziffern einzeln draufaddieren:
         while (len > 0)
-        { // erg_MSDptr/erg_len/erg_LSDptr ist eine NUDS, erg_len < need.
-          var uintB ch = *(const uintB *)MSBptr; MSBptr++; // nächstes Character
-          if (!(ch=='.')) // Punkt überlesen
-            { // Wert von ch ('0'-'9','A'-'Z','a'-'z') bilden:
+          { // erg_MSDptr/erg_len/erg_LSDptr is a NUDS, erg_len < need.
+            var uintB ch = *(const uintB *)MSBptr; MSBptr++; // next character
+            if (!(ch=='.')) // skip decimal point
+              { // Compute value of ('0'-'9','A'-'Z','a'-'z'):
                 ch = ch - '0';
-              if (ch > '9'-'0') // keine Ziffer?
+                if (ch > '9'-'0') // not a digit?
                   { ch = ch+'0'-'A'+10;
-                  if (ch > 'Z'-'A'+10) // kein Großbuchstabe?
-                    { ch = ch+'A'-'a'; } // dann ein Kleinbuchstabe
+                    if (ch > 'Z'-'A'+10) // not an uppercase letter?
+                      { ch = ch+'A'-'a'; } // must be lowercase!
                   }
-              // multipliziere erg mit base und addiere ch:
+                // multiply erg with base and add ch:
                {var uintD carry = mulusmall_loop_lsp(base,erg_LSDptr,erg_len,ch);
                 if (!(carry==0))
-                // muß NUDS vergrößern:
+                  // need to extend NUDS:
                   { lsprefnext(erg_MSDptr) = carry; erg_len++; }
               }}
             len--;
           }
+      }
       return NUDS_to_I(erg_MSDptr,erg_len);
 }