git: c58c77246f88 - main - [libm] Avoid left shift of signed integer entities

The branch main has been updated by dim:

URL: https://cgit.FreeBSD.org/src/commit/?id=c58c77246f88da87f309e8c449e98195d43e2c76

commit c58c77246f88da87f309e8c449e98195d43e2c76
Author:     Steve Kargl <kargl@FreeBSD.org>
AuthorDate: 2025-08-14 18:38:41 +0000
Commit:     Dimitry Andric <dim@FreeBSD.org>
CommitDate: 2025-08-14 18:38:41 +0000

    [libm] Avoid left shift of signed integer entities
    
    Follow-up commit d180086e6eae by fixing the left shift of signed integer
    entities through the use of a helper function. Specific per file changes
    are:
    
    * lib/msun/src/e_fmodf.c:
    * lib/msun/src/s_remquof.c:
      . Eliminate now unused variable 'i'.
      . Sort declaration statement.
      . Use subnormal_ilogbf() to avoid left shift of signed integer.
    
    * lib/msun/src/math_private.h b/lib/msun/src/math_private.h:
      . Implement subnormal_ilogbf() to extract an exponent of a subnormal
        float.  This avoids left shifts of signed integers.
      . Update nearby comment.
    
    * lib/msun/src/s_ilogbf.c
      . Fix declaration of the function statement in accordance with style(9).
      . Use subnormal_ilogbf() to avoid left shift of signed integer.
    
    PR:             288850
    MFC after:      1 week
---
 lib/msun/src/e_fmodf.c      | 16 +++++++++-------
 lib/msun/src/math_private.h | 16 +++++++++++++++-
 lib/msun/src/s_ilogbf.c     |  5 +++--
 lib/msun/src/s_remquof.c    | 16 +++++++++-------
 4 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/lib/msun/src/e_fmodf.c b/lib/msun/src/e_fmodf.c
index a7d1a0c22acd..ada969db44c7 100644
--- a/lib/msun/src/e_fmodf.c
+++ b/lib/msun/src/e_fmodf.c
@@ -27,7 +27,7 @@ static const float one = 1.0, Zero[] = {0.0, -0.0,};
 float
 fmodf(float x, float y)
 {
-	int32_t n,hx,hy,hz,ix,iy,sx,i;
+	int32_t hx, hy, hz, ix, iy, n, sx;
 
 	GET_FLOAT_WORD(hx,x);
 	GET_FLOAT_WORD(hy,y);
@@ -44,14 +44,16 @@ fmodf(float x, float y)
 	    return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
 
     /* determine ix = ilogb(x) */
-	if(hx<0x00800000) {	/* subnormal x */
-	    for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
-	} else ix = (hx>>23)-127;
+	if(hx<0x00800000)
+	    ix = subnormal_ilogbf(hx);
+	else
+	    ix = (hx>>23)-127;
 
     /* determine iy = ilogb(y) */
-	if(hy<0x00800000) {	/* subnormal y */
-	    for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
-	} else iy = (hy>>23)-127;
+	if(hy<0x00800000)
+	    iy = subnormal_ilogbf(hy);
+	else
+	    iy = (hy>>23)-127;
 
     /* set up {hx,lx}, {hy,ly} and align y to x */
 	if(ix >= -126)
diff --git a/lib/msun/src/math_private.h b/lib/msun/src/math_private.h
index 0711f2f33c41..fbd84e246ca7 100644
--- a/lib/msun/src/math_private.h
+++ b/lib/msun/src/math_private.h
@@ -740,7 +740,7 @@ irintl(long double x)
 } while (0)
 
 /*
- * For a double entity split into high and low parts, compute ilogb.
+ * For a subnormal double entity split into high and low parts, compute ilogb.
  */
 static inline int32_t
 subnormal_ilogb(int32_t hi, int32_t lo)
@@ -760,6 +760,20 @@ subnormal_ilogb(int32_t hi, int32_t lo)
 	return (j);
 }
 
+/*
+ * For a subnormal float entity represented as an int32_t, compute ilogb.
+ */
+static inline int32_t
+subnormal_ilogbf(int32_t hx)
+{
+	int32_t j;
+	uint32_t i;
+	i = (uint32_t) hx << 8;
+	for (j = -126; i < 0x7fffffff; i <<= 1) j -=1;
+
+	return (j);
+}
+
 #ifdef DEBUG
 #if defined(__amd64__) || defined(__i386__)
 #define	breakpoint()	asm("int $3")
diff --git a/lib/msun/src/s_ilogbf.c b/lib/msun/src/s_ilogbf.c
index e0f8fee26ac8..5195e2331af3 100644
--- a/lib/msun/src/s_ilogbf.c
+++ b/lib/msun/src/s_ilogbf.c
@@ -18,7 +18,8 @@
 #include "math.h"
 #include "math_private.h"
 
-	int ilogbf(float x)
+int
+ilogbf(float x)
 {
 	int32_t hx,ix;
 
@@ -28,7 +29,7 @@
 	    if(hx==0)
 		return FP_ILOGB0;
 	    else			/* subnormal x */
-	        for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1;
+		ix = subnormal_ilogbf(hx);
 	    return ix;
 	}
 	else if (hx<0x7f800000) return (hx>>23)-127;
diff --git a/lib/msun/src/s_remquof.c b/lib/msun/src/s_remquof.c
index 9cd148586796..e4adb8321559 100644
--- a/lib/msun/src/s_remquof.c
+++ b/lib/msun/src/s_remquof.c
@@ -25,7 +25,7 @@ static const float Zero[] = {0.0, -0.0,};
 float
 remquof(float x, float y, int *quo)
 {
-	int32_t n,hx,hy,hz,ix,iy,sx,i;
+	int32_t hx, hy, hz, ix, iy, n, sx;
 	u_int32_t q,sxy;
 
 	GET_FLOAT_WORD(hx,x);
@@ -47,14 +47,16 @@ remquof(float x, float y, int *quo)
 	}
 
     /* determine ix = ilogb(x) */
-	if(hx<0x00800000) {	/* subnormal x */
-	    for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
-	} else ix = (hx>>23)-127;
+	if(hx<0x00800000)
+	    ix = subnormal_ilogbf(hx);
+	else
+	    ix = (hx>>23)-127;
 
     /* determine iy = ilogb(y) */
-	if(hy<0x00800000) {	/* subnormal y */
-	    for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
-	} else iy = (hy>>23)-127;
+	if(hy<0x00800000)
+	    iy = subnormal_ilogbf(hy);
+	else
+	    iy = (hy>>23)-127;
 
     /* set up {hx,lx}, {hy,ly} and align y to x */
 	if(ix >= -126)