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[PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead local conversion, and reduce branches

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  [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead local conversion, and reduce branches zengzhaoxiu@163.com - 2016-06-29 18:30 +0200
    Re: [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead  local conversion, and reduce branches Alexey Dobriyan <adobriyan@gmail.com> - 2016-06-30 00:10 +0200
      Re: [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead  local conversion, and reduce branches Zhaoxiu Zeng <zengzhaoxiu@163.com> - 2016-06-30 16:50 +0200

#1433895 — [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead local conversion, and reduce branches

From: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>

Signed-off-by: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
---
 lib/kstrtox.c | 22 +++++-----------------
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/lib/kstrtox.c b/lib/kstrtox.c
index d8a5cf6..70d3374 100644
--- a/lib/kstrtox.c
+++ b/lib/kstrtox.c
@@ -48,38 +48,26 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
 {
 	unsigned long long res;
 	unsigned int rv;
-	int overflow;
+	unsigned int overflow;
+	unsigned int val;
 
 	res = 0;
 	rv = 0;
 	overflow = 0;
-	while (*s) {
-		unsigned int val;
-
-		if ('0' <= *s && *s <= '9')
-			val = *s - '0';
-		else if ('a' <= _tolower(*s) && _tolower(*s) <= 'f')
-			val = _tolower(*s) - 'a' + 10;
-		else
-			break;
-
-		if (val >= base)
-			break;
+	while ((val = hex_to_bin(*s++)) < base) {
 		/*
 		 * Check for overflow only if we are within range of
 		 * it in the max base we support (16)
 		 */
 		if (unlikely(res & (~0ull << 60))) {
 			if (res > div_u64(ULLONG_MAX - val, base))
-				overflow = 1;
+				overflow = KSTRTOX_OVERFLOW;
 		}
 		res = res * base + val;
 		rv++;
-		s++;
 	}
 	*p = res;
-	if (overflow)
-		rv |= KSTRTOX_OVERFLOW;
+	rv |= overflow;
 	return rv;
 }
 
-- 
2.7.4

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#1434079 — Re: [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead local conversion, and reduce branches

On Thu, Jun 30, 2016 at 12:22:13AM +0800, zengzhaoxiu@163.com wrote:
> --- a/lib/kstrtox.c
> +++ b/lib/kstrtox.c
> @@ -48,38 +48,26 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
>  {
>  	unsigned long long res;
>  	unsigned int rv;
> -	int overflow;
> +	unsigned int overflow;
> +	unsigned int val;
>  
>  	res = 0;
>  	rv = 0;
>  	overflow = 0;
> -	while (*s) {
> -		unsigned int val;
> -
> -		if ('0' <= *s && *s <= '9')
> -			val = *s - '0';
> -		else if ('a' <= _tolower(*s) && _tolower(*s) <= 'f')
> -			val = _tolower(*s) - 'a' + 10;
> -		else
> -			break;
> -
> -		if (val >= base)
> -			break;
> +	while ((val = hex_to_bin(*s++)) < base) {

I hate this function. And it has a branch if your table patch doesn't
go it. And it is beartrap (unsigned int = -1 < base).

ACK *s++ bit, though. Should make code smaller in my experience.
Please, change to "unsigned char c; while ((c = *s++)".
This is about maximum code compression I can understand.

>  		/*
>  		 * Check for overflow only if we are within range of
>  		 * it in the max base we support (16)
>  		 */
>  		if (unlikely(res & (~0ull << 60))) {
>  			if (res > div_u64(ULLONG_MAX - val, base))
> -				overflow = 1;
> +				overflow = KSTRTOX_OVERFLOW;

Just do |= KSTRTOX_OVERFLOW here directly, it is the leftmost bit.

>  		}
>  		res = res * base + val;
>  		rv++;
> -		s++;
>  	}
>  	*p = res;
> -	if (overflow)
> -		rv |= KSTRTOX_OVERFLOW;
> +	rv |= overflow;
>  	return rv;
>  }

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#1434636 — Re: [PATCH 2/2] lib: kstrtox: _parse_integer: use hex_to_bin instead local conversion, and reduce branches

On 2016/6/30 6:06, Alexey Dobriyan wrote:
> On Thu, Jun 30, 2016 at 12:22:13AM +0800, zengzhaoxiu@163.com wrote:
>> --- a/lib/kstrtox.c
>> +++ b/lib/kstrtox.c
>> @@ -48,38 +48,26 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
>>  {
>>  	unsigned long long res;
>>  	unsigned int rv;
>> -	int overflow;
>> +	unsigned int overflow;
>> +	unsigned int val;
>>  
>>  	res = 0;
>>  	rv = 0;
>>  	overflow = 0;
>> -	while (*s) {
>> -		unsigned int val;
>> -
>> -		if ('0' <= *s && *s <= '9')
>> -			val = *s - '0';
>> -		else if ('a' <= _tolower(*s) && _tolower(*s) <= 'f')
>> -			val = _tolower(*s) - 'a' + 10;
>> -		else
>> -			break;
>> -
>> -		if (val >= base)
>> -			break;
>> +	while ((val = hex_to_bin(*s++)) < base) {
> I hate this function. And it has a branch if your table patch doesn't
> go it. And it is beartrap (unsigned int = -1 < base).

How about this?

for (;;) {
    unsigned int val = hex_to_bin(*s++);
    if (val >= base)
        break;

> ACK *s++ bit, though. Should make code smaller in my experience.
> Please, change to "unsigned char c; while ((c = *s++)".
> This is about maximum code compression I can understand.

The previous tests are useless until reach the end of s.
The '\0' will be caught by "if (val >= base)" too.

>>  		/*
>>  		 * Check for overflow only if we are within range of
>>  		 * it in the max base we support (16)
>>  		 */
>>  		if (unlikely(res & (~0ull << 60))) {
>>  			if (res > div_u64(ULLONG_MAX - val, base))
>> -				overflow = 1;
>> +				overflow = KSTRTOX_OVERFLOW;
> Just do |= KSTRTOX_OVERFLOW here directly, it is the leftmost bit.

I thought so too at first， but finally I decided to reserve the varaible "overflow",
because this hack depend on the definition of KSTRTOX_OVERFLOW.

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