Remove redundant emptiness check from genericParseNumber

https://bugs.webkit.org/show_bug.cgi?id=285184
rdar://142083712

Reviewed by Darin Adler.

Merge: https://source.chromium.org/chromium/chromium/src/+/ab685d36561909a7ef373183f37fc3d6fc21bb83

When the 'start = buffer.position()' condition was reached we could be sure that we
had already consumed at least one character - one of '.' or '0'-'9' or
whitespace (potentially also '+'/'-' as a prefix) - and that even holds
true moving the definition of |start| after consuming any leading
whitespace. The reason for this is the up-front check for any character
in the set '0'-'9' or '.'.
Remove the redundant checks - replacing them with an assert - while
moving the definition of 'start' so that it doesn't point before any
leading whitespace.

* Source/WebCore/svg/SVGParserUtilities.cpp:
(WebCore::genericParseNumber):

Canonical link: https://commits.webkit.org/292567@main

Author: Ahmad-S792

Source/WebCore/svg/SVGParserUtilities.cpp

@@ -3,6 +3,7 @@
  * Copyright (C) 2006 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2007-2024 Apple Inc. All rights reserved.
+ * Copyright (C) 2016 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ -51,7 +52,6 @@ template <typename CharacterType, typename FloatType = float> static std::option
     FloatType exponent = 0;
     int sign = 1;
     int expsign = 1;
-    auto start = buffer.position();
 
     // read the sign
     if (buffer.hasCharactersRemaining() && *buffer == '+')
@@ -65,16 +65,16 @@ template <typename CharacterType, typename FloatType = float> static std::option
         return std::nullopt;
 
     // read the integer part, build right-to-left
-    auto spanStartIntPart = buffer.span();
+    auto spanDigitsStart = buffer.span();
 
     // Advance to first non-digit.
     skipWhile<isASCIIDigit>(buffer);
 
-    if (buffer.position() > spanStartIntPart.data()) {
-        size_t indexScanIntPart = buffer.position() - spanStartIntPart.data();
+    if (buffer.position() > spanDigitsStart.data()) {
+        size_t indexScanIntPart = buffer.position() - spanDigitsStart.data();
         FloatType multiplier = 1;
         for (size_t i = indexScanIntPart; i > 0; --i) {
-            integer += multiplier * static_cast<FloatType>(spanStartIntPart[i - 1] - '0');
+            integer += multiplier * static_cast<FloatType>(spanDigitsStart[i - 1] - '0');
             multiplier *= 10;
         }
         // Bail out early if this overflows.
@@ -94,8 +94,12 @@ template <typename CharacterType, typename FloatType = float> static std::option
             decimal += (*(buffer++) - '0') * (frac *= static_cast<FloatType>(0.1));
     }
 
+    // When we get here we should have consumed either a digit for the integer
+    // part or a fractional part (with at least one digit after the '.'.)
+    ASSERT(spanDigitsStart.data() != buffer.position());
+
     // read the exponent part
-    if (buffer.position() != start && buffer.span().size() > 1 && (*buffer == 'e' || *buffer == 'E')
+    if (buffer.span().size() > 1 && (*buffer == 'e' || *buffer == 'E')
         && (buffer[1] != 'x' && buffer[1] != 'm')) {
         ++buffer;
 
@@ -130,9 +134,6 @@ template <typename CharacterType, typename FloatType = float> static std::option
     if (!isValidRange(number))
         return std::nullopt;
 
-    if (start == buffer.position())
-        return std::nullopt;
-
     if (skip == SuffixSkippingPolicy::Skip)
         skipOptionalSVGSpacesOrDelimiter(buffer);