X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fmath%2Ffma.c;h=17f1cdcc39bc2a7671b99dbeb7d107ee7973d505;hb=8224bdbbedc60a5d637d95ddd344501f667f0294;hp=a9de2cb37e0f70d73312edeadec8fbd6a21c9992;hpb=b1cbd70743f0e0e0295e92c3e38d7599114db8c6;p=musl

diff --git a/src/math/fma.c b/src/math/fma.c
index a9de2cb3..17f1cdcc 100644
--- a/src/math/fma.c
+++ b/src/math/fma.c
@@ -23,10 +23,6 @@ static void add(long double *hi, long double *lo, long double x, long double y)
 	*lo = y - r;
 }
 
-/*
-TODO(nsz): probably simpler mul is enough if we assume x and y are doubles
-so last 11bits are all zeros, no subnormals etc
-*/
 /* exact mul, assumes no over/underflow */
 static void mul(long double *hi, long double *lo, long double x, long double y)
 {
@@ -45,7 +41,7 @@ static void mul(long double *hi, long double *lo, long double x, long double y)
 
 /*
 assume (long double)(hi+lo) == hi
-return an adjusted hi so that rounding it to double is correct
+return an adjusted hi so that rounding it to double (or less) precision is correct
 */
 static long double adjust(long double hi, long double lo)
 {
@@ -59,17 +55,25 @@ static long double adjust(long double hi, long double lo)
 	ulo.x = lo;
 	if (uhi.bits.s == ulo.bits.s)
 		uhi.bits.m++;
-	else
+	else {
 		uhi.bits.m--;
+		/* handle underflow and take care of ld80 implicit msb */
+		if (uhi.bits.m == (uint64_t)-1/2) {
+			uhi.bits.m *= 2;
+			uhi.bits.e--;
+		}
+	}
 	return uhi.x;
 }
 
+/* adjusted add so the result is correct when rounded to double (or less) precision */
 static long double dadd(long double x, long double y)
 {
 	add(&x, &y, x, y);
 	return adjust(x, y);
 }
 
+/* adjusted mul so the result is correct when rounded to double (or less) precision */
 static long double dmul(long double x, long double y)
 {
 	mul(&x, &y, x, y);
@@ -85,6 +89,7 @@ static int getexp(long double x)
 
 double fma(double x, double y, double z)
 {
+	#pragma STDC FENV_ACCESS ON
 	long double hi, lo1, lo2, xy;
 	int round, ez, exy;
 
@@ -115,7 +120,7 @@ double fma(double x, double y, double z)
 		add(&hi, &lo2, xy, z);
 		if (hi == 0) {
 			fesetround(round);
-			/* TODO: verify that the sign of 0 is always correct */
+			/* make sure that the sign of 0 is correct */
 			return (xy + z) + lo1;
 		}
 	} else {
@@ -251,7 +256,7 @@ static inline double add_and_denormalize(double a, double b, int scale)
 			INSERT_WORD64(sum.hi, hibits);
 		}
 	}
-	return (ldexp(sum.hi, scale));
+	return scalbn(sum.hi, scale);
 }
 
 /*
@@ -302,6 +307,7 @@ static inline struct dd dd_mul(double a, double b)
  */
 double fma(double x, double y, double z)
 {
+	#pragma STDC FENV_ACCESS ON
 	double xs, ys, zs, adj;
 	struct dd xy, r;
 	int oround;
@@ -368,7 +374,7 @@ double fma(double x, double y, double z)
 		}
 	}
 	if (spread <= DBL_MANT_DIG * 2)
-		zs = ldexp(zs, -spread);
+		zs = scalbn(zs, -spread);
 	else
 		zs = copysign(DBL_MIN, zs);
 
@@ -394,7 +400,7 @@ double fma(double x, double y, double z)
 		 */
 		fesetround(oround);
 		volatile double vzs = zs; /* XXX gcc CSE bug workaround */
-		return (xy.hi + vzs + ldexp(xy.lo, spread));
+		return xy.hi + vzs + scalbn(xy.lo, spread);
 	}
 
 	if (oround != FE_TONEAREST) {
@@ -404,13 +410,13 @@ double fma(double x, double y, double z)
 		 */
 		fesetround(oround);
 		adj = r.lo + xy.lo;
-		return (ldexp(r.hi + adj, spread));
+		return scalbn(r.hi + adj, spread);
 	}
 
 	adj = add_adjusted(r.lo, xy.lo);
 	if (spread + ilogb(r.hi) > -1023)
-		return (ldexp(r.hi + adj, spread));
+		return scalbn(r.hi + adj, spread);
 	else
-		return (add_and_denormalize(r.hi, adj, spread));
+		return add_and_denormalize(r.hi, adj, spread);
 }
 #endif