parser: Accelerate and improve object parsing

Scan characters ahead of time in order to accelerate parsing.
This also solves various problem parsing units inside expressions, or
detecting error conditions such as `1.0+`.

While the functional improvements are numerous, the performance one is
just not there, for a reason that remains to be investigated:

Time to parse `DEMO.48S`, as measured by running `TEval` on
`« "/STATE/DEMO.48S" RCL »`:

Before: 358ms (DM32) 259ms (DM42)
 After: 427ms (DM32) 349ms (DM42)

Note that the main objective is not just performance, but also
improving battery life by reducing CPU utilization for a very common
operation. So it matters that we do not have a regression.

Fixes: #940

Signed-off-by: Christophe de Dinechin <[email protected]>

Author: c3d

src/bignum.cc

@@ -102,15 +102,6 @@ integer_p bignum::as_integer() const
 }
 
 
-PARSE_BODY(bignum)
-// ----------------------------------------------------------------------------
-//    Bignums are parsed by integer parser, so we can skip here
-// ----------------------------------------------------------------------------
-{
-    return SKIP;
-}
-
-
 HELP_BODY(bignum)
 // ----------------------------------------------------------------------------
 //    Help topic for big integers

src/bignum.h

@@ -194,7 +194,6 @@ struct bignum : text
 
 public:
     OBJECT_DECL(bignum);
-    PARSE_DECL(bignum);
     RENDER_DECL(bignum);
     HELP_DECL(bignum);
 };

src/command.cc

@@ -65,11 +65,6 @@ PARSE_BODY(command)
 //    Try to parse this as a command, using either short or long name
 // ----------------------------------------------------------------------------
 {
-    // We scan all the commands in one loop under 'Drop'. Skip all other
-    id i = p.candidate;
-    if (i != ID_Drop)
-        return SKIP;
-
     bool    eq     = p.precedence;
     id      type   = id(0);
     id      found  = id(0);
@@ -113,8 +108,8 @@ PARSE_BODY(command)
     }
 
     record(command,
-           "Parsing [%s] with id %u %+s (%+s), found %u len %u",
-           ref, i, name(i), fancy(i), found, len);
+           "Parsing [%s] found %u %+s %+s len %u",
+           ref, found, name(found), fancy(found), len);
 
     if (!found)
         return SKIP;