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commit    3de359f18f2bfbc96272bd265264aa5c2f247ca4
Author:   John Naylor <john.naylor@postgresql.org>
Date:     Fri Jul 08 07:53:20 2022 +0000
First released in: 16.0

    Simplify json lexing state
    
    Instead of updating the length as we go, use a const pointer to end of
    the input, which we know already at the start.
    
    This simplifies the coding and may improve performance slightly, but
    the real motivation for doing this is to make further changes in this
    area easier to reason about.
    
    Discussion: https://www.postgresql.org/message-id/CAFBsxsGhaR2KQ5eisaK%3D6Vm60t%3DaxhD8Ckj1qFoCH1pktZi%2B2w%40mail.gmail.com


 src/common/jsonapi.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/src/common/jsonapi.c b/src/common/jsonapi.c
index 98e4ef09426..eeedc0645a0 100644
--- a/src/common/jsonapi.c
+++ b/src/common/jsonapi.c
@@ -519,26 +519,23 @@ JsonParseErrorType
 json_lex(JsonLexContext *lex)
 {
 	char	   *s;
-	int			len;
+	char	   *const end = lex->input + lex->input_length;
 	JsonParseErrorType result;
 
 	/* Skip leading whitespace. */
 	s = lex->token_terminator;
-	len = s - lex->input;
-	while (len < lex->input_length &&
-		   (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r'))
+	while (s < end && (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r'))
 	{
 		if (*s++ == '\n')
 		{
 			++lex->line_number;
 			lex->line_start = s;
 		}
-		len++;
 	}
 	lex->token_start = s;
 
 	/* Determine token type. */
-	if (len >= lex->input_length)
+	if (s >= end)
 	{
 		lex->token_start = NULL;
 		lex->prev_token_terminator = lex->token_terminator;
@@ -623,7 +620,7 @@ json_lex(JsonLexContext *lex)
 					 * the whole word as an unexpected token, rather than just
 					 * some unintuitive prefix thereof.
 					 */
-					for (p = s; p - s < lex->input_length - len && JSON_ALPHANUMERIC_CHAR(*p); p++)
+					for (p = s; p < end && JSON_ALPHANUMERIC_CHAR(*p); p++)
 						 /* skip */ ;
 
 					/*
@@ -672,7 +669,7 @@ static inline JsonParseErrorType
 json_lex_string(JsonLexContext *lex)
 {
 	char	   *s;
-	int			len;
+	char	   *const end = lex->input + lex->input_length;
 	int			hi_surrogate = -1;
 
 	if (lex->strval != NULL)
@@ -680,13 +677,11 @@ json_lex_string(JsonLexContext *lex)
 
 	Assert(lex->input_length > 0);
 	s = lex->token_start;
-	len = lex->token_start - lex->input;
 	for (;;)
 	{
 		s++;
-		len++;
 		/* Premature end of the string. */
-		if (len >= lex->input_length)
+		if (s >= end)
 		{
 			lex->token_terminator = s;
 			return JSON_INVALID_TOKEN;
@@ -704,8 +699,7 @@ json_lex_string(JsonLexContext *lex)
 		{
 			/* OK, we have an escape character. */
 			s++;
-			len++;
-			if (len >= lex->input_length)
+			if (s >= end)
 			{
 				lex->token_terminator = s;
 				return JSON_INVALID_TOKEN;
@@ -718,8 +712,7 @@ json_lex_string(JsonLexContext *lex)
 				for (i = 1; i <= 4; i++)
 				{
 					s++;
-					len++;
-					if (len >= lex->input_length)
+					if (s >= end)
 					{
 						lex->token_terminator = s;
 						return JSON_INVALID_TOKEN;


[parent: 3140f089855c]