Better formatting of Cr<> label for real valued drivers.

Rework the encoding of a real value in the Cr<> label to be similar to
the format used by the %loadi/wr instruction. This mantissa-expoment
format better carries all the bits of the desired real value with
plenty of fidelity and range.

tgt-vvp/vvp_scope.c

@@ -22,6 +22,7 @@
 # include  <malloc.h>
 #endif
 # include  <stdlib.h>
+# include  <math.h>
 # include  <string.h>
 # include  <inttypes.h>
 # include  <assert.h>
@@ -468,6 +469,42 @@ static char* draw_C8_to_string(ivl_net_const_t cptr,
       return result;
 }
 
+static char* draw_Cr_to_string(ivl_net_const_t cptr)
+{
+      char tmp[256];
+
+      double value = ivl_const_real(cptr);
+      uint64_t mant = 0;
+
+      if (isinf(value)) {
+	    if (value > 0)
+		  snprintf(tmp, sizeof(tmp), "Cr<m0g3fff>");
+	    else
+		  snprintf(tmp, sizeof(tmp), "Cr<m0g7fff>");
+	    return strdup(tmp);
+      }
+
+      int sign = 0;
+      if (value < 0) {
+	    sign = 0x4000;
+	    value *= -1;
+      }
+
+      int expo;
+      double fract = frexp(value, &expo);
+      fract = ldexp(fract, 63);
+      mant = fract;
+      expo -= 63;
+
+      int vexp = expo + 0x1000;
+      assert(vexp >= 0);
+      assert(vexp < 0x2000);
+      vexp += sign;
+
+      snprintf(tmp, sizeof(tmp), "Cr<m%" PRIx64 "g%x>", mant, vexp);
+      return strdup(tmp);
+}
+
 /*
  * This function takes a nexus and looks for an input functor. It then
  * draws to the output a string that represents that functor. What we
@@ -604,11 +641,7 @@ static char* draw_net_input_drive(ivl_nexus_t nex, ivl_nexus_ptr_t nptr)
 		  break;
 
 		case IVL_VT_REAL:
-		    { char tmp[256];
+		  result = draw_Cr_to_string(cptr);
-		      snprintf(tmp, sizeof(tmp),
-			       "Cr<%lg>", ivl_const_real(cptr));
-		      result = strdup(tmp);
-		    }
 		  break;
 
 		default:

vvp/compile.cc

@@ -815,14 +815,43 @@ void input_connect(vvp_net_t*fdx, unsigned port, char*label)
 	    return;
       }
 
+	/* Handle the Cr<> constant driver, which is a real-value
+	   driver. The format is broken into mantissa and
+	   exponent. The exponent in turn includes a sign bit.
+
+	   The mantissa is a 64bit integer value (encoded in hex).
+
+	   The exponent included the sign bit (0x4000) and the binary
+	   exponent offset by 0x1000. The actual exponent is the
+	   encoded exponent - 0x1000.
+
+	   The real value is sign * (mant ** exp).  */
       if ((strncmp(label, "Cr<", 3) == 0)
 	  && ((tp = strchr(label,'>')))
 	  && (tp[1] == 0)
-	  && (strspn(label+3, "0123456789.-e")+3 == (unsigned)(tp-label))) {
+	  && (strspn(label+3, "0123456789abcdefmg")+3 == (unsigned)(tp-label))) {
+
+	    char*cp = label+3;
+	    assert(*cp == 'm');
+	    cp += 1;
+	    uint64_t mant = strtoull(cp, &cp, 16);
+	    assert(*cp == 'g');
+	    cp += 1;
+	    int exp = strtoul(cp, 0, 16);
 
 	    double tmp;
+	    if (mant == 0 && exp == 0x3fff) {
+		  tmp = INFINITY;
+	    } else if (mant == 0 && exp == 0x7fff) {
+		  tmp = -INFINITY;
+	    } else if (exp == 0x3fff) {
+		  tmp = nan("");
+	    } else {
+		  double sign = (exp & 0x4000)? -1.0 : 1.0;
+		  exp &= 0x1fff;
 
-	    sscanf(label+3, "%lg", &tmp);
+		  tmp = sign * ldexp((double)mant, exp - 0x1000);
+	    }
 
 	    schedule_set_vector(ifdx, tmp);
 	    free(label);

vvp/lexor.lex

@@ -199,7 +199,7 @@
       assert(yylval.text);
       return T_SYMBOL; }
 
-"Cr<"[.$_a-zA-Z0-9/,\-]*">" {
+"Cr<m"[a-f0-9]*"x"[a-f0-9]*">" {
       yylval.text = strdup(yytext);
       assert(yylval.text);
       return T_SYMBOL; }