improve posint morphisms

morphisms/posint.morphism-base

@@ -14,9 +14,9 @@ morph_nat_as_u64_to_pos ()
     return 0;
 ```
 
-morph_nat_as_u64_to_pos ()
+morph_nat_as_pos_to_u64 (Endianness:Type)
       ℕ
-    ~ <PosInt 0 LittleEndian>
+    ~ <PosInt 0 Endianness>
     ~ <Seq~<LengthPrefix x86.UInt64> <Digit 0>~x86.UInt64>
 -->   ℕ
     ~ x86.UInt64
@@ -42,14 +42,16 @@ morph_posint_radix_le (SrcRadix:ℤ, DstRadix:ℤ)
 
     length_prefix_uint64_array_clear( dst );
 
-    if( DstRadix == 0 ) {
+    #if DstRadix==0
         length_prefix_uint64_array_push( dst, value );
-    } else if( DstRadix > 0 ) {
-        while( value > 0 ) {
+    #else
+        if( value == 0 ) {
+            length_prefix_uint64_array_push( dst, 0 );
+        } else while( value > 0 ) {
             length_prefix_uint64_array_push( dst, value % DstRadix );
             value /= DstRadix;
         }
-    }
+    #endif
 
     return 0;
 ```
@@ -69,13 +71,16 @@ morph_posint_radix_be (SrcRadix:ℤ, DstRadix:ℤ)
         value += src->items[i];
     }
 
-    if( DstRadix == 0 ) {
+    #if DstRadix==0
         dst->len = 1;
         dst->items[0] = value;
-    } else {
+    #else
         uint64_t v = value;
         dst->len = 0;
-        while( v ) {
+
+        if( v == 0 ) {
+            dst->len = 1;
+        } else while( v ) {
             dst->len++;
             v /= DstRadix;
         }
@@ -85,7 +90,7 @@ morph_posint_radix_be (SrcRadix:ℤ, DstRadix:ℤ)
             dst->items[--i] = value % DstRadix;
             value /= DstRadix;
         }
-    }
+    #endif
 
     return 0;
 ```