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Subject: bug#33144: Replace some loops with str functions
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Thread-Topic: Replace some loops with str functions
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Hi,

I'm writing a program analysis that tries to find and replace some loops wi=
th str* functions. I'm trying to see if these replacements are a useful ref=
actoring or the loops are intentional. I noticed that diff has a couple of =
these loops and wrote a patch (pasted below) that changes this.

I find strspn easier to read, communicate intention and has less LOC, but w=
ould be interested to hear why you would like to keep the loops to.

Cheers,
Timotej

From 38e7030f127f567fd2d02f27663168dde4472d57 Mon Sep 17 00:00:00 2001
From: Timotej Kapus <tk1713@HIDDEN>
Date: Wed, 24 Oct 2018 23:47:22 +0100
Subject: [PATCH] maint: change 3 loops to strspn calls

  * src/ifdef.c: Change 3 loops to equivalent calls to strspn
---
 src/ifdef.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/ifdef.c b/src/ifdef.c
index 0ecc2c0..8046ac5 100644
--- a/src/ifdef.c
+++ b/src/ifdef.c
@@ -313,13 +313,10 @@ do_printf_spec (FILE *out, char const *spec,
   /* Scan printf-style SPEC of the form %[-'0]*[0-9]*(.[0-9]*)?[cdoxX].  *=
/
   /* assert (*f =3D=3D '%'); */
   f++;
-  while ((c =3D *f++) =3D=3D '-' || c =3D=3D '\'' || c =3D=3D '0')
-    continue;
-  while (ISDIGIT (c))
-    c =3D *f++;
-  if (c =3D=3D '.')
-    while (ISDIGIT (c =3D *f++))
-      continue;
+  f +=3D strspn(f, "-\'0") + 1;
+  f +=3D strspn(f, "0123456789") + 1;
+  if ((c =3D *f++) =3D=3D '.')
+    f +=3D strspn(f, "0123456789") + 1;
   c1 =3D *f++;

   switch (c)
--
2.7.4





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<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Diso-8859-=
2">
<style type=3D"text/css" style=3D"display:none;"><!-- P {margin-top:0;margi=
n-bottom:0;} --></style>
</head>
<body dir=3D"ltr">
<div id=3D"divtagdefaultwrapper" style=3D"font-size:12pt;color:#000000;font=
-family:Calibri,Helvetica,sans-serif;" dir=3D"ltr">
<p style=3D"margin-top:0;margin-bottom:0"></p>
<div>Hi,&nbsp;<br>
<br>
I'm writing a program analysis that tries to find and replace some loops wi=
th str* functions. I'm trying to see if these replacements are a useful ref=
actoring or the loops are intentional. I noticed that diff has a couple of =
these loops and wrote a patch (pasted
 below) that changes this.</div>
<div><br>
</div>
<div>I find strspn easier to read, communicate intention and has less LOC, =
but would be interested to hear why you would like to keep the loops to.</d=
iv>
<div><br>
</div>
<div>Cheers,</div>
<div>Timotej</div>
<div><br>
</div>
<div>
<div>
<div>From 38e7030f127f567fd2d02f27663168dde4472d57 Mon Sep 17 00:00:00 2001=
</div>
<div>From: Timotej Kapus &lt;tk1713@HIDDEN&gt;</div>
<div>Date: Wed, 24 Oct 2018 23:47:22 &#43;0100</div>
<div>Subject: [PATCH] maint: change 3 loops to strspn calls</div>
<div><br>
</div>
<div>&nbsp; * src/ifdef.c: Change 3 loops to equivalent calls to strspn</di=
v>
<div>---</div>
<div>&nbsp;src/ifdef.c | 11 &#43;&#43;&#43;&#43;-------</div>
<div>&nbsp;1 file changed, 4 insertions(&#43;), 7 deletions(-)</div>
<div><br>
</div>
<div>diff --git a/src/ifdef.c b/src/ifdef.c</div>
<div>index 0ecc2c0..8046ac5 100644</div>
<div>--- a/src/ifdef.c</div>
<div>&#43;&#43;&#43; b/src/ifdef.c</div>
<div>@@ -313,13 &#43;313,10 @@ do_printf_spec (FILE *out, char const *spec,=
</div>
<div>&nbsp; &nbsp;/* Scan printf-style SPEC of the form %[-'0]*[0-9]*(.[0-9=
]*)?[cdoxX].&nbsp; */</div>
<div>&nbsp; &nbsp;/* assert (*f =3D=3D '%'); */</div>
<div>&nbsp; &nbsp;f&#43;&#43;;</div>
<div>-&nbsp; while ((c =3D *f&#43;&#43;) =3D=3D '-' || c =3D=3D '\'' || c =
=3D=3D '0')</div>
<div>-&nbsp; &nbsp; continue;</div>
<div>-&nbsp; while (ISDIGIT (c))</div>
<div>-&nbsp; &nbsp; c =3D *f&#43;&#43;;</div>
<div>-&nbsp; if (c =3D=3D '.')</div>
<div>-&nbsp; &nbsp; while (ISDIGIT (c =3D *f&#43;&#43;))</div>
<div>-&nbsp; &nbsp; &nbsp; continue;</div>
<div>&#43;&nbsp; f &#43;=3D strspn(f, &quot;-\'0&quot;) &#43; 1;</div>
<div>&#43;&nbsp; f &#43;=3D strspn(f, &quot;0123456789&quot;) &#43; 1;</div=
>
<div>&#43;&nbsp; if ((c =3D *f&#43;&#43;) =3D=3D '.')</div>
<div>&#43;&nbsp; &nbsp; f &#43;=3D strspn(f, &quot;0123456789&quot;) &#43; =
1;</div>
<div>&nbsp; &nbsp;c1 =3D *f&#43;&#43;;</div>
<div><br>
</div>
<div>&nbsp; &nbsp;switch (c)</div>
<div>--</div>
<div>2.7.4</div>
<br>
</div>
<div></div>
<div><br>
</div>
<br>
</div>
<br>
<p></p>
</div>
</body>
</html>

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Subject: bug#33144: Acknowledgement (Replace some loops with str functions)
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Subject: bug#33144: [bug-diffutils] bug#33144: Replace some loops with str functions
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On 10/24/18 4:06 PM, Kapus, Timotej wrote:
> I find strspn easier to read, communicate intention and has less LOC

On the other hand, it's probably slower for this particular use case, 
and the replacement code you wrote is not equivalent to the code it 
replaced because 'c' ends up having a different value.

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Subject: bug#33144: [bug-diffutils] bug#33144: Replace some loops with str functions
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Thanks for your reply and apologies for sending a buggy patch. Yes I agree =
it's probably slower, but I doubt it has significant impact on the whole ru=
ntime. The insignifcant slowdown might be worth it, if you would find the c=
ode much clearer. In any case, I'm attaching an updated version of the patc=
h, where I  proved c and c1 are eqvivalent at the end, up to the bound of 5=
 bytes, so should be fine this time.


From 4911d9676f1914fb4691061887396f2b21a0d036 Mon Sep 17 00:00:00 2001
From: Timotej Kapus <tk1713@HIDDEN>
Date: Wed, 24 Oct 2018 23:47:22 +0100
Subject: [PATCH] maint: change 3 loops to strspn calls

  * src/ifdef.c: Change 3 loops to equivalent calls to strspn
---
 src/ifdef.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/ifdef.c b/src/ifdef.c
index 0ecc2c0..4533e3a 100644
--- a/src/ifdef.c
+++ b/src/ifdef.c
@@ -313,13 +313,13 @@ do_printf_spec (FILE *out, char const *spec,
   /* Scan printf-style SPEC of the form %[-'0]*[0-9]*(.[0-9]*)?[cdoxX].  *=
/
   /* assert (*f =3D=3D '%'); */
   f++;
-  while ((c =3D *f++) =3D=3D '-' || c =3D=3D '\'' || c =3D=3D '0')
-    continue;
-  while (ISDIGIT (c))
-    c =3D *f++;
-  if (c =3D=3D '.')
-    while (ISDIGIT (c =3D *f++))
-      continue;
+  f +=3D strspn(f, "-\'0") + 1;
+  if(ISDIGIT(c =3D *(f - 1)))
+    f +=3D strspn(f, "0123456789") + 1;
+  if ((c =3D *(f - 1)) =3D=3D '.') {
+    f +=3D strspn(f, "0123456789") + 1;
+    c =3D *(f - 1);
+  }
   c1 =3D *f++;

   switch (c)
--
2.7.4



________________________________
Od: Paul Eggert <eggert@HIDDEN>
Poslano: =E8etrtek, 25. oktober 2018 20:57:10
Za: Kapus, Timotej; 33144 <at> debbugs.gnu.org
Kp: Cadar, Cristian
Zadeva: Re: [bug-diffutils] bug#33144: Replace some loops with str function=
s

On 10/24/18 4:06 PM, Kapus, Timotej wrote:
> I find strspn easier to read, communicate intention and has less LOC

On the other hand, it's probably slower for this particular use case,
and the replacement code you wrote is not equivalent to the code it
replaced because 'c' ends up having a different value.


--_000_AMSPR06MB2623188ECD44B00E2D7773AD5F00AMSPR06MB262eurprd_
Content-Type: text/html; charset="iso-8859-2"
Content-Transfer-Encoding: quoted-printable

<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Diso-8859-=
2">
<style type=3D"text/css" style=3D"display:none;"><!-- P {margin-top:0;margi=
n-bottom:0;} --></style>
</head>
<body dir=3D"ltr">
<div id=3D"divtagdefaultwrapper" style=3D"font-size:12pt;color:#000000;font=
-family:Calibri,Helvetica,sans-serif;" dir=3D"ltr">
<p style=3D"margin-top:0;margin-bottom:0">Thanks for your reply and apologi=
es for sending a buggy patch. Yes I agree it's probably slower, but I doubt=
 it has significant impact on the whole runtime. The insignifcant slowdown =
might be worth it, if you would find
 the code much clearer. In any case, I'm attaching an updated version of th=
e patch, where I &nbsp;proved c and c1 are eqvivalent at the end, up to the=
 bound of 5 bytes, so should be fine this time.</p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p style=3D"margin-top:0;margin-bottom:0"></p>
<div>From 4911d9676f1914fb4691061887396f2b21a0d036 Mon Sep 17 00:00:00 2001=
</div>
<div>From: Timotej Kapus &lt;tk1713@HIDDEN&gt;</div>
<div>Date: Wed, 24 Oct 2018 23:47:22 &#43;0100</div>
<div>Subject: [PATCH] maint: change 3 loops to strspn calls</div>
<div><br>
</div>
<div>&nbsp; * src/ifdef.c: Change 3 loops to equivalent calls to strspn</di=
v>
<div>---</div>
<div>&nbsp;src/ifdef.c | 14 &#43;&#43;&#43;&#43;&#43;&#43;&#43;-------</div=
>
<div>&nbsp;1 file changed, 7 insertions(&#43;), 7 deletions(-)</div>
<div><br>
</div>
<div>diff --git a/src/ifdef.c b/src/ifdef.c</div>
<div>index 0ecc2c0..4533e3a 100644</div>
<div>--- a/src/ifdef.c</div>
<div>&#43;&#43;&#43; b/src/ifdef.c</div>
<div>@@ -313,13 &#43;313,13 @@ do_printf_spec (FILE *out, char const *spec,=
</div>
<div>&nbsp; &nbsp;/* Scan printf-style SPEC of the form %[-'0]*[0-9]*(.[0-9=
]*)?[cdoxX].&nbsp; */</div>
<div>&nbsp; &nbsp;/* assert (*f =3D=3D '%'); */</div>
<div>&nbsp; &nbsp;f&#43;&#43;;</div>
<div>-&nbsp; while ((c =3D *f&#43;&#43;) =3D=3D '-' || c =3D=3D '\'' || c =
=3D=3D '0')</div>
<div>-&nbsp; &nbsp; continue;</div>
<div>-&nbsp; while (ISDIGIT (c))</div>
<div>-&nbsp; &nbsp; c =3D *f&#43;&#43;;</div>
<div>-&nbsp; if (c =3D=3D '.')</div>
<div>-&nbsp; &nbsp; while (ISDIGIT (c =3D *f&#43;&#43;))</div>
<div>-&nbsp; &nbsp; &nbsp; continue;</div>
<div>&#43;&nbsp; f &#43;=3D strspn(f, &quot;-\'0&quot;) &#43; 1;</div>
<div>&#43;&nbsp; if(ISDIGIT(c =3D *(f - 1)))</div>
<div>&#43;&nbsp; &nbsp; f &#43;=3D strspn(f, &quot;0123456789&quot;) &#43; =
1;</div>
<div>&#43;&nbsp; if ((c =3D *(f - 1)) =3D=3D '.') {</div>
<div>&#43;&nbsp; &nbsp; f &#43;=3D strspn(f, &quot;0123456789&quot;) &#43; =
1;</div>
<div>&#43;&nbsp; &nbsp; c =3D *(f - 1);</div>
<div>&#43;&nbsp; }</div>
<div>&nbsp; &nbsp;c1 =3D *f&#43;&#43;;</div>
<div>&nbsp;</div>
<div>&nbsp; &nbsp;switch (c)</div>
<div>--&nbsp;</div>
<div>2.7.4</div>
<div><br>
</div>
<br>
<p></p>
</div>
<hr style=3D"display:inline-block;width:98%" tabindex=3D"-1">
<div id=3D"divRplyFwdMsg" dir=3D"ltr"><font face=3D"Calibri, sans-serif" st=
yle=3D"font-size:11pt" color=3D"#000000"><b>Od:</b> Paul Eggert &lt;eggert@=
cs.ucla.edu&gt;<br>
<b>Poslano:</b> =E8etrtek, 25. oktober 2018 20:57:10<br>
<b>Za:</b> Kapus, Timotej; 33144 <at> debbugs.gnu.org<br>
<b>Kp:</b> Cadar, Cristian<br>
<b>Zadeva:</b> Re: [bug-diffutils] bug#33144: Replace some loops with str f=
unctions</font>
<div>&nbsp;</div>
</div>
<div class=3D"BodyFragment"><font size=3D"2"><span style=3D"font-size:11pt;=
">
<div class=3D"PlainText">On 10/24/18 4:06 PM, Kapus, Timotej wrote:<br>
&gt; I find strspn easier to read, communicate intention and has less LOC<b=
r>
<br>
On the other hand, it's probably slower for this particular use case, <br>
and the replacement code you wrote is not equivalent to the code it <br>
replaced because 'c' ends up having a different value.<br>
<br>
</div>
</span></font></div>
</body>
</html>

--_000_AMSPR06MB2623188ECD44B00E2D7773AD5F00AMSPR06MB262eurprd_--

Last modified: Mon, 25 Nov 2019 12:00:02 UTC

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