Re: script to find incorrect tests on unsigneds

[Matthew Wilcox <matthew@wil.cx>]

On Fri, Apr 18, 2008 at 09:08:55PM +0200, Julia Lawall wrote:
> I found 63 occurrences of this problem with the following semantic match
> (http://www.emn.fr/x-info/coccinelle/):
> 
> @@ unsigned int i; @@
> 
> * i < 0
> 
> I looked through all of the results by hand, and they all seem to be 
> problems.  In many cases, it seems like the variable should not be 
> unsigned as it is used to hold the return value of a function that might 
> return a negative error code, but I haven't looked into this in detail.
> 
> In the output below, the lines that begin with a single start contain a 
> test of whether an unsigned variable or structure field is less than 0.
> The output is actually generated with diff, but I converted the -s to *s 
> to avoid confusion.

> diff -u -p a/drivers/spi/spi_s3c24xx.c b/drivers/spi/spi_s3c24xx.c
> *** a/drivers/spi/spi_s3c24xx.c 2008-03-12 14:13:14.000000000 +0100
> @@ -127,7 +127,7 @@ static int s3c24xx_spi_setupxfer(struct 
>  
>  	div = (div / 2) - 1;
>  
> *	if (div < 0)
>  		div = 1;
>  
>  	if (div > 255)

Since this one's always in the range 0-255, it could probably be made
signed, but it's just as easy to make it work unsigned.

Reported-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --git a/drivers/spi/spi_s3c24xx.c b/drivers/spi/spi_s3c24xx.c
index b7476b8..b398cc9 100644
--- a/drivers/spi/spi_s3c24xx.c
+++ b/drivers/spi/spi_s3c24xx.c
@@ -125,10 +125,10 @@ static int s3c24xx_spi_setupxfer(struct spi_device *spi,
 	/* is clk = pclk / (2 * (pre+1)), or is it
 	 *    clk = (pclk * 2) / ( pre + 1) */
 
-	div = (div / 2) - 1;
+	div /= 2;
 
-	if (div < 0)
-		div = 1;
+	if (div > 0)
+		div -= 1;
 
 	if (div > 255)
 		div = 255;

-- 
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