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* [PATCH] lib/zstd: Fix bitwise vs logical operators
@ 2021-08-15  0:41 Nathan Chancellor
  2021-08-16 15:14 ` David Sterba
  2021-08-17  1:05 ` Andrew Morton
  0 siblings, 2 replies; 6+ messages in thread
From: Nathan Chancellor @ 2021-08-15  0:41 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Nick Desaulniers, linux-kernel, clang-built-linux, Nathan Chancellor

clang warns several times along the lines of:

lib/zstd/compress.c:1043:7: warning: bitwise and of boolean expressions; did you mean logical and? [-Wbool-operation-and]
                if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                   &&

Bitwise ANDs do not short circuit, meaning that the ZSTD_read32 calls
will be evaluated even if the first condition is not true. This is not
always a problem but it is not a standard way to do conditionals so
replace the bitwise ANDs with logical ones to fix the warning and make
the code clearer.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 lib/zstd/compress.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/lib/zstd/compress.c b/lib/zstd/compress.c
index b080264ed3ad..0e515d1d4237 100644
--- a/lib/zstd/compress.c
+++ b/lib/zstd/compress.c
@@ -1040,7 +1040,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
 		const BYTE *match = base + matchIndex;
 		hashTable[h] = curr; /* update hash table */
 
-		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
+		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
 			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
 			ip++;
 			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
@@ -1072,7 +1072,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
 			hashTable[ZSTD_hashPtr(base + curr + 2, hBits, mls)] = curr + 2; /* here because curr+2 could be > iend-8 */
 			hashTable[ZSTD_hashPtr(ip - 2, hBits, mls)] = (U32)(ip - 2 - base);
 			/* check immediate repcode */
-			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
+			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
 				/* store sequence */
 				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
 				{
@@ -1291,7 +1291,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
 		const BYTE *match = base + matchIndexS;
 		hashLong[h2] = hashSmall[h] = curr; /* update hash tables */
 
-		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
+		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
 			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
 			ip++;
 			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
@@ -1350,7 +1350,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
 			hashLong[ZSTD_hashPtr(ip - 2, hBitsL, 8)] = hashSmall[ZSTD_hashPtr(ip - 2, hBitsS, mls)] = (U32)(ip - 2 - base);
 
 			/* check immediate repcode */
-			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
+			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
 				/* store sequence */
 				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
 				{
@@ -1929,7 +1929,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
 		const BYTE *start = ip + 1;
 
 		/* check repCode */
-		if ((offset_1 > 0) & (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
+		if ((offset_1 > 0) && (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
 			/* repcode : we take it */
 			matchLength = ZSTD_count(ip + 1 + EQUAL_READ32, ip + 1 + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
 			if (depth == 0)
@@ -1953,7 +1953,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
 		if (depth >= 1)
 			while (ip < ilimit) {
 				ip++;
-				if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
+				if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
 					size_t const mlRep = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
 					int const gain2 = (int)(mlRep * 3);
 					int const gain1 = (int)(matchLength * 3 - ZSTD_highbit32((U32)offset + 1) + 1);
@@ -1974,7 +1974,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
 				/* let's find an even better one */
 				if ((depth == 2) && (ip < ilimit)) {
 					ip++;
-					if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
+					if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
 						size_t const ml2 = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
 						int const gain2 = (int)(ml2 * 4);
 						int const gain1 = (int)(matchLength * 4 - ZSTD_highbit32((U32)offset + 1) + 1);
@@ -2021,7 +2021,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
 		}
 
 		/* check immediate repcode */
-		while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
+		while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
 			/* store sequence */
 			matchLength = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_2, iend) + EQUAL_READ32;
 			offset = offset_2;

base-commit: ba31f97d43be41ca99ab72a6131d7c226306865f
-- 
2.33.0.rc2


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] lib/zstd: Fix bitwise vs logical operators
  2021-08-15  0:41 [PATCH] lib/zstd: Fix bitwise vs logical operators Nathan Chancellor
@ 2021-08-16 15:14 ` David Sterba
  2021-08-16 16:53   ` Nathan Chancellor
  2021-08-17  1:05 ` Andrew Morton
  1 sibling, 1 reply; 6+ messages in thread
From: David Sterba @ 2021-08-16 15:14 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Andrew Morton, Nick Desaulniers, linux-kernel, clang-built-linux,
	terrelln

You should CC Nick Terell for ZSTD patches, added.

On Sat, Aug 14, 2021 at 05:41:54PM -0700, Nathan Chancellor wrote:
> clang warns several times along the lines of:
> 
> lib/zstd/compress.c:1043:7: warning: bitwise and of boolean expressions; did you mean logical and? [-Wbool-operation-and]
>                 if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>                                    &&
> 
> Bitwise ANDs do not short circuit, meaning that the ZSTD_read32 calls
> will be evaluated even if the first condition is not true. This is not
> always a problem but it is not a standard way to do conditionals so
> replace the bitwise ANDs with logical ones to fix the warning and make
> the code clearer.
> 
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  lib/zstd/compress.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/lib/zstd/compress.c b/lib/zstd/compress.c
> index b080264ed3ad..0e515d1d4237 100644
> --- a/lib/zstd/compress.c
> +++ b/lib/zstd/compress.c
> @@ -1040,7 +1040,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
>  		const BYTE *match = base + matchIndex;
>  		hashTable[h] = curr; /* update hash table */
>  
> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>  			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
>  			ip++;
>  			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
> @@ -1072,7 +1072,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
>  			hashTable[ZSTD_hashPtr(base + curr + 2, hBits, mls)] = curr + 2; /* here because curr+2 could be > iend-8 */
>  			hashTable[ZSTD_hashPtr(ip - 2, hBits, mls)] = (U32)(ip - 2 - base);
>  			/* check immediate repcode */
> -			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
> +			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>  				/* store sequence */
>  				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
>  				{
> @@ -1291,7 +1291,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
>  		const BYTE *match = base + matchIndexS;
>  		hashLong[h2] = hashSmall[h] = curr; /* update hash tables */
>  
> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
>  			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
>  			ip++;
>  			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
> @@ -1350,7 +1350,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
>  			hashLong[ZSTD_hashPtr(ip - 2, hBitsL, 8)] = hashSmall[ZSTD_hashPtr(ip - 2, hBitsS, mls)] = (U32)(ip - 2 - base);
>  
>  			/* check immediate repcode */
> -			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
> +			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>  				/* store sequence */
>  				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
>  				{
> @@ -1929,7 +1929,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>  		const BYTE *start = ip + 1;
>  
>  		/* check repCode */
> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
>  			/* repcode : we take it */
>  			matchLength = ZSTD_count(ip + 1 + EQUAL_READ32, ip + 1 + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>  			if (depth == 0)
> @@ -1953,7 +1953,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>  		if (depth >= 1)
>  			while (ip < ilimit) {
>  				ip++;
> -				if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
> +				if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>  					size_t const mlRep = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>  					int const gain2 = (int)(mlRep * 3);
>  					int const gain1 = (int)(matchLength * 3 - ZSTD_highbit32((U32)offset + 1) + 1);
> @@ -1974,7 +1974,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>  				/* let's find an even better one */
>  				if ((depth == 2) && (ip < ilimit)) {
>  					ip++;
> -					if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
> +					if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>  						size_t const ml2 = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>  						int const gain2 = (int)(ml2 * 4);
>  						int const gain1 = (int)(matchLength * 4 - ZSTD_highbit32((U32)offset + 1) + 1);
> @@ -2021,7 +2021,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>  		}
>  
>  		/* check immediate repcode */
> -		while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
> +		while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>  			/* store sequence */
>  			matchLength = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_2, iend) + EQUAL_READ32;
>  			offset = offset_2;
> 
> base-commit: ba31f97d43be41ca99ab72a6131d7c226306865f
> -- 
> 2.33.0.rc2

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] lib/zstd: Fix bitwise vs logical operators
  2021-08-16 15:14 ` David Sterba
@ 2021-08-16 16:53   ` Nathan Chancellor
  2021-08-16 21:17     ` David Sterba
  0 siblings, 1 reply; 6+ messages in thread
From: Nathan Chancellor @ 2021-08-16 16:53 UTC (permalink / raw)
  To: dsterba, Andrew Morton, Nick Desaulniers, linux-kernel,
	clang-built-linux, terrelln

On 8/16/2021 8:14 AM, David Sterba wrote:
> You should CC Nick Terell for ZSTD patches, added.

Thanks for the info and adding him, I did not see an entry for lib/zstd/ 
in MAINTAINERS and there is no consistent person picking up patches 
according to git.

Cheers,
Nathan

> On Sat, Aug 14, 2021 at 05:41:54PM -0700, Nathan Chancellor wrote:
>> clang warns several times along the lines of:
>>
>> lib/zstd/compress.c:1043:7: warning: bitwise and of boolean expressions; did you mean logical and? [-Wbool-operation-and]
>>                  if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>>                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>                                     &&
>>
>> Bitwise ANDs do not short circuit, meaning that the ZSTD_read32 calls
>> will be evaluated even if the first condition is not true. This is not
>> always a problem but it is not a standard way to do conditionals so
>> replace the bitwise ANDs with logical ones to fix the warning and make
>> the code clearer.
>>
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>> ---
>>   lib/zstd/compress.c | 16 ++++++++--------
>>   1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/zstd/compress.c b/lib/zstd/compress.c
>> index b080264ed3ad..0e515d1d4237 100644
>> --- a/lib/zstd/compress.c
>> +++ b/lib/zstd/compress.c
>> @@ -1040,7 +1040,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
>>   		const BYTE *match = base + matchIndex;
>>   		hashTable[h] = curr; /* update hash table */
>>   
>> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>>   			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
>>   			ip++;
>>   			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
>> @@ -1072,7 +1072,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
>>   			hashTable[ZSTD_hashPtr(base + curr + 2, hBits, mls)] = curr + 2; /* here because curr+2 could be > iend-8 */
>>   			hashTable[ZSTD_hashPtr(ip - 2, hBits, mls)] = (U32)(ip - 2 - base);
>>   			/* check immediate repcode */
>> -			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>> +			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>>   				/* store sequence */
>>   				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
>>   				{
>> @@ -1291,7 +1291,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
>>   		const BYTE *match = base + matchIndexS;
>>   		hashLong[h2] = hashSmall[h] = curr; /* update hash tables */
>>   
>> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
>> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) { /* note : by construction, offset_1 <= curr */
>>   			mLength = ZSTD_count(ip + 1 + 4, ip + 1 + 4 - offset_1, iend) + 4;
>>   			ip++;
>>   			ZSTD_storeSeq(seqStorePtr, ip - anchor, anchor, 0, mLength - MINMATCH);
>> @@ -1350,7 +1350,7 @@ void ZSTD_compressBlock_doubleFast_generic(ZSTD_CCtx *cctx, const void *src, siz
>>   			hashLong[ZSTD_hashPtr(ip - 2, hBitsL, 8)] = hashSmall[ZSTD_hashPtr(ip - 2, hBitsS, mls)] = (U32)(ip - 2 - base);
>>   
>>   			/* check immediate repcode */
>> -			while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>> +			while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>>   				/* store sequence */
>>   				size_t const rLength = ZSTD_count(ip + 4, ip + 4 - offset_2, iend) + 4;
>>   				{
>> @@ -1929,7 +1929,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>>   		const BYTE *start = ip + 1;
>>   
>>   		/* check repCode */
>> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
>> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1) == ZSTD_read32(ip + 1 - offset_1))) {
>>   			/* repcode : we take it */
>>   			matchLength = ZSTD_count(ip + 1 + EQUAL_READ32, ip + 1 + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>>   			if (depth == 0)
>> @@ -1953,7 +1953,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>>   		if (depth >= 1)
>>   			while (ip < ilimit) {
>>   				ip++;
>> -				if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>> +				if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>>   					size_t const mlRep = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>>   					int const gain2 = (int)(mlRep * 3);
>>   					int const gain1 = (int)(matchLength * 3 - ZSTD_highbit32((U32)offset + 1) + 1);
>> @@ -1974,7 +1974,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>>   				/* let's find an even better one */
>>   				if ((depth == 2) && (ip < ilimit)) {
>>   					ip++;
>> -					if ((offset) && ((offset_1 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>> +					if ((offset) && ((offset_1 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_1)))) {
>>   						size_t const ml2 = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_1, iend) + EQUAL_READ32;
>>   						int const gain2 = (int)(ml2 * 4);
>>   						int const gain1 = (int)(matchLength * 4 - ZSTD_highbit32((U32)offset + 1) + 1);
>> @@ -2021,7 +2021,7 @@ void ZSTD_compressBlock_lazy_generic(ZSTD_CCtx *ctx, const void *src, size_t src
>>   		}
>>   
>>   		/* check immediate repcode */
>> -		while ((ip <= ilimit) && ((offset_2 > 0) & (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>> +		while ((ip <= ilimit) && ((offset_2 > 0) && (ZSTD_read32(ip) == ZSTD_read32(ip - offset_2)))) {
>>   			/* store sequence */
>>   			matchLength = ZSTD_count(ip + EQUAL_READ32, ip + EQUAL_READ32 - offset_2, iend) + EQUAL_READ32;
>>   			offset = offset_2;
>>
>> base-commit: ba31f97d43be41ca99ab72a6131d7c226306865f
>> -- 
>> 2.33.0.rc2

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] lib/zstd: Fix bitwise vs logical operators
  2021-08-16 16:53   ` Nathan Chancellor
@ 2021-08-16 21:17     ` David Sterba
  0 siblings, 0 replies; 6+ messages in thread
From: David Sterba @ 2021-08-16 21:17 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Andrew Morton, Nick Desaulniers, linux-kernel, clang-built-linux,
	terrelln

On Mon, Aug 16, 2021 at 09:53:53AM -0700, Nathan Chancellor wrote:
> On 8/16/2021 8:14 AM, David Sterba wrote:
> > You should CC Nick Terell for ZSTD patches, added.
> 
> Thanks for the info and adding him, I did not see an entry for lib/zstd/ 
> in MAINTAINERS and there is no consistent person picking up patches 
> according to git.

It's in an intermediate state [1], so far the compression algorithms
have been under the crypto subsystem because it's part of the API, but
regarding ZSTD, it's a bigger beast IMHO deserving an independent git
and merge flow, so I just noticed.

[1] https://lwn.net/ml/linux-kernel/20210430013157.747152-1-nickrterrell@gmail.com/

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] lib/zstd: Fix bitwise vs logical operators
  2021-08-15  0:41 [PATCH] lib/zstd: Fix bitwise vs logical operators Nathan Chancellor
  2021-08-16 15:14 ` David Sterba
@ 2021-08-17  1:05 ` Andrew Morton
  2021-08-19 21:22   ` David Laight
  1 sibling, 1 reply; 6+ messages in thread
From: Andrew Morton @ 2021-08-17  1:05 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Nick Desaulniers, linux-kernel, clang-built-linux, terrelln

On Sat, 14 Aug 2021 17:41:54 -0700 Nathan Chancellor <nathan@kernel.org> wrote:

> clang warns several times along the lines of:
> 
> lib/zstd/compress.c:1043:7: warning: bitwise and of boolean expressions; did you mean logical and? [-Wbool-operation-and]
>                 if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>                                    &&
> 
> Bitwise ANDs do not short circuit, meaning that the ZSTD_read32 calls
> will be evaluated even if the first condition is not true. This is not
> always a problem but it is not a standard way to do conditionals so
> replace the bitwise ANDs with logical ones to fix the warning and make
> the code clearer.
> 
> ...
>
> --- a/lib/zstd/compress.c
> +++ b/lib/zstd/compress.c
> @@ -1040,7 +1040,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t sr
>  		const BYTE *match = base + matchIndex;
>  		hashTable[h] = curr; /* update hash table */
>  
> -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
> +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {

yeah, this is a late night party trick which is sometimes used to
attempt to speed things up by avoiding a branch.  It is perhaps
beneficial if the LHS is almost always true.  I guess.

I'd prefer that the code not do this - it's silly, looks wrong and I
bet it's unmeasurable.

But I think this code is supposed to be kept in sync with an
out-of-tree upstream version so this change might be problematic.

Dunno, let's see what Nick thinks.


^ permalink raw reply	[flat|nested] 6+ messages in thread

* RE: [PATCH] lib/zstd: Fix bitwise vs logical operators
  2021-08-17  1:05 ` Andrew Morton
@ 2021-08-19 21:22   ` David Laight
  0 siblings, 0 replies; 6+ messages in thread
From: David Laight @ 2021-08-19 21:22 UTC (permalink / raw)
  To: 'Andrew Morton', Nathan Chancellor
  Cc: Nick Desaulniers, linux-kernel, clang-built-linux, terrelln

From: Andrew Morton
> Sent: 17 August 2021 02:06
> 
> On Sat, 14 Aug 2021 17:41:54 -0700 Nathan Chancellor <nathan@kernel.org> wrote:
> 
> > clang warns several times along the lines of:
> >
> > lib/zstd/compress.c:1043:7: warning: bitwise and of boolean expressions; did you mean logical and?
> [-Wbool-operation-and]
> >                 if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
> >                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >                                    &&
> >
> > Bitwise ANDs do not short circuit, meaning that the ZSTD_read32 calls
> > will be evaluated even if the first condition is not true. This is not
> > always a problem but it is not a standard way to do conditionals so
> > replace the bitwise ANDs with logical ones to fix the warning and make
> > the code clearer.
> >
> > ...
> >
> > --- a/lib/zstd/compress.c
> > +++ b/lib/zstd/compress.c
> > @@ -1040,7 +1040,7 @@ void ZSTD_compressBlock_fast_generic(ZSTD_CCtx *cctx, const void *src, size_t
> sr
> >  		const BYTE *match = base + matchIndex;
> >  		hashTable[h] = curr; /* update hash table */
> >
> > -		if ((offset_1 > 0) & (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
> > +		if ((offset_1 > 0) && (ZSTD_read32(ip + 1 - offset_1) == ZSTD_read32(ip + 1))) {
> 
> yeah, this is a late night party trick which is sometimes used to
> attempt to speed things up by avoiding a branch.  It is perhaps
> beneficial if the LHS is almost always true.  I guess.
> 
> I'd prefer that the code not do this - it's silly, looks wrong and I
> bet it's unmeasurable.
> 
> But I think this code is supposed to be kept in sync with an
> out-of-tree upstream version so this change might be problematic.

Except that in this case you want the short-circuit.
The RH condition is slow and always true when offset_1 is zero.
OTOH subtracting offset_1 makes the lines look odd (out of context).

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-08-19 21:23 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-15  0:41 [PATCH] lib/zstd: Fix bitwise vs logical operators Nathan Chancellor
2021-08-16 15:14 ` David Sterba
2021-08-16 16:53   ` Nathan Chancellor
2021-08-16 21:17     ` David Sterba
2021-08-17  1:05 ` Andrew Morton
2021-08-19 21:22   ` David Laight

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