pp_length: code tidy and simplify assert

The STATIC_ASSERT_STMT() is basically checking that shifting the
HINT_BYTES byte left 26 places gives you SVf_UTF8, so just assert that.
There's no need to assert the current values of HINT_BYTES and SVf_UTF8.

Other than that, this commit tides up the code a bit (only whitespace
changes and unnecessary brace removal), and adds/updates some code comments.

1 files changed, 26 insertions, 15 deletions

diff --git a/pp.c b/pp.c
index 016b7e82de..24326b8d63 100644
--- a/pp.c
+++ b/pp.c
@@ -3230,22 +3230,29 @@ PP(pp_oct)
 
 /* String stuff. */
 
+
 PP(pp_length)
 {
     dSP; dTARGET;
     SV * const sv = TOPs;
 
     U32 in_bytes = IN_BYTES;
-    /* simplest case shortcut */
-    /* turn off SVf_UTF8 in tmp flags if HINT_BYTES on*/
+    /* Simplest case shortcut:
+     * set svflags to just the SVf_POK|SVs_GMG|SVf_UTF8 from the SV,
+     * with the SVf_UTF8 flag inverted if under 'use bytes' (HINT_BYTES
+     * set)
+     */
     U32 svflags = (SvFLAGS(sv) ^ (in_bytes << 26)) & (SVf_POK|SVs_GMG|SVf_UTF8);
-    STATIC_ASSERT_STMT(HINT_BYTES == 0x00000008 && SVf_UTF8 == 0x20000000 && (SVf_UTF8 == HINT_BYTES << 26));
+
+    STATIC_ASSERT_STMT(SVf_UTF8 == (HINT_BYTES << 26));
     SETs(TARG);
 
-    if(LIKELY(svflags == SVf_POK))
+    if (LIKELY(svflags == SVf_POK))
         goto simple_pv;
-    if(svflags & SVs_GMG)
+
+    if (svflags & SVs_GMG)
         mg_get(sv);
+
     if (SvOK(sv)) {
         STRLEN len;
 	if (!IN_BYTES) { /* reread to avoid using an C auto/register */
@@ -3253,30 +3260,34 @@ PP(pp_length)
                 goto simple_pv;
 	    len = sv_len_utf8_nomg(sv);
         }
-	else
-	{
+	else {
             /* unrolled SvPV_nomg_const(sv,len) */
-            if(SvPOK_nog(sv)){
-                simple_pv:
+            if (SvPOK_nog(sv)) {
+              simple_pv:
                 len = SvCUR(sv);
-            } else  {
+            }
+            else {
                 (void)sv_2pv_flags(sv, &len, 0|SV_CONST_RETURN);
             }
 	}
         TARGi((IV)(len), 1);
-    } else {
+    }
+    else {
 	if (!SvPADTMP(TARG)) {
+            /* OPpTARGET_MY: targ is var in '$lex = length()' */
             sv_set_undef(TARG);
             SvSETMAGIC(TARG);
-	} else { /* TARG is on stack at this point and is overwriten by SETs.
-                   This branch is the odd one out, so put TARG by default on
-                   stack earlier to let local SP go out of liveness sooner */
+	}
+        else
+            /* TARG is on stack at this point and is overwriten by SETs.
+             * This branch is the odd one out, so put TARG by default on
+             * stack earlier to let local SP go out of liveness sooner */
             SETs(&PL_sv_undef);
-        }
     }
     return NORMAL; /* no putback, SP didn't move in this opcode */
 }
 
+
 /* Returns false if substring is completely outside original string.
    No length is indicated by len_iv = 0 and len_is_uv = 0.  len_is_uv must
    always be true for an explicit 0.