[libc][math] Add tests and fix some issues with FTZ/DAZ modes. (#113744)

Author: lntue

libc/src/math/generic/atan2.cpp

@@ -230,8 +230,8 @@ LLVM_LIBC_FUNCTION(double, atan2, (double y, double x)) {
   if (LIBC_UNLIKELY(max_exp > 0x7ffU - 128U || min_exp < 128U)) {
     if (x_bits.is_nan() || y_bits.is_nan())
       return FPBits::quiet_nan().get_val();
-    unsigned x_except = x_abs == 0 ? 0 : (FPBits(x_abs).is_inf() ? 2 : 1);
-    unsigned y_except = y_abs == 0 ? 0 : (FPBits(y_abs).is_inf() ? 2 : 1);
+    unsigned x_except = x == 0.0 ? 0 : (FPBits(x_abs).is_inf() ? 2 : 1);
+    unsigned y_except = y == 0.0 ? 0 : (FPBits(y_abs).is_inf() ? 2 : 1);
 
     // Exceptional cases:
     //   EXCEPT[y_except][x_except][x_is_neg]

libc/src/math/generic/cbrt.cpp

@@ -151,9 +151,10 @@ LLVM_LIBC_FUNCTION(double, cbrt, (double x)) {
 
   if (LIBC_UNLIKELY(x_abs < FPBits::min_normal().uintval() ||
                     x_abs >= FPBits::inf().uintval())) {
-    if (x_abs == 0 || x_abs >= FPBits::inf().uintval())
+    if (x == 0.0 || x_abs >= FPBits::inf().uintval())
       // x is 0, Inf, or NaN.
-      return x;
+      // Make sure it works for FTZ/DAZ modes.
+      return static_cast<double>(x + x);
 
     // x is non-zero denormal number.
     // Normalize x.

libc/src/math/generic/cbrtf.cpp

@@ -93,9 +93,10 @@ LLVM_LIBC_FUNCTION(float, cbrtf, (float x)) {
   uint32_t x_abs = x_bits.uintval() & 0x7fff'ffff;
   uint32_t sign_bit = (x_bits.uintval() >> 31) << DoubleBits::EXP_LEN;
 
-  if (LIBC_UNLIKELY(x_abs == 0 || x_abs >= 0x7f80'0000)) {
+  if (LIBC_UNLIKELY(x == 0.0f || x_abs >= 0x7f80'0000)) {
     // x is 0, Inf, or NaN.
-    return x;
+    // Make sure it works for FTZ/DAZ modes.
+    return x + x;
   }
 
   double xd = static_cast<double>(x);

libc/src/math/generic/log.cpp

@@ -749,7 +749,7 @@ LLVM_LIBC_FUNCTION(double, log, (double x)) {
 
   if (LIBC_UNLIKELY(xbits.uintval() < FPBits_t::min_normal().uintval() ||
                     xbits.uintval() > FPBits_t::max_normal().uintval())) {
-    if (xbits.is_zero()) {
+    if (x == 0.0) {
       // return -Inf and raise FE_DIVBYZERO.
       fputil::set_errno_if_required(ERANGE);
       fputil::raise_except_if_required(FE_DIVBYZERO);

libc/src/math/generic/log10.cpp

@@ -751,7 +751,7 @@ LLVM_LIBC_FUNCTION(double, log10, (double x)) {
 
   if (LIBC_UNLIKELY(xbits.uintval() < FPBits_t::min_normal().uintval() ||
                     xbits.uintval() > FPBits_t::max_normal().uintval())) {
-    if (xbits.is_zero()) {
+    if (x == 0.0) {
       // return -Inf and raise FE_DIVBYZERO.
       fputil::set_errno_if_required(ERANGE);
       fputil::raise_except_if_required(FE_DIVBYZERO);

libc/src/math/generic/log10f.cpp

@@ -164,7 +164,7 @@ LLVM_LIBC_FUNCTION(float, log10f, (float x)) {
 
   if (LIBC_UNLIKELY(x_u < FPBits::min_normal().uintval() ||
                     x_u > FPBits::max_normal().uintval())) {
-    if (xbits.is_zero()) {
+    if (x == 0.0f) {
       // Return -inf and raise FE_DIVBYZERO
       fputil::set_errno_if_required(ERANGE);
       fputil::raise_except_if_required(FE_DIVBYZERO);

libc/src/math/generic/log1p.cpp

@@ -927,8 +927,8 @@ LLVM_LIBC_FUNCTION(double, log1p, (double x)) {
       //   log(1 + x) = nextafter(x, -inf) for FE_DOWNWARD, or
       //                                       FE_TOWARDZERO and x > 0,
       //              = x                  otherwise.
-      if (LIBC_UNLIKELY(xbits.is_zero()))
-        return x;
+      if (x == 0.0)
+        return x + x; // Handle FTZ/DAZ correctly.
 
       volatile float tp = 1.0f;
       volatile float tn = -1.0f;
@@ -943,7 +943,7 @@ LLVM_LIBC_FUNCTION(double, log1p, (double x)) {
         return FPBits_t(x_u + 1).get_val();
       }
 
-      return x;
+      return (x + x == 0.0) ? x + x : x;
     }
     x_dd = fputil::exact_add(1.0, x);
   }

libc/src/math/generic/log2.cpp

@@ -871,7 +871,7 @@ LLVM_LIBC_FUNCTION(double, log2, (double x)) {
 
   if (LIBC_UNLIKELY(xbits.uintval() < FPBits_t::min_normal().uintval() ||
                     xbits.uintval() > FPBits_t::max_normal().uintval())) {
-    if (xbits.is_zero()) {
+    if (x == 0.0) {
       // return -Inf and raise FE_DIVBYZERO.
       fputil::set_errno_if_required(ERANGE);
       fputil::raise_except_if_required(FE_DIVBYZERO);

libc/src/math/generic/log2f.cpp

@@ -72,7 +72,7 @@ LLVM_LIBC_FUNCTION(float, log2f, (float x)) {
   // Exceptional inputs.
   if (LIBC_UNLIKELY(x_u < FPBits::min_normal().uintval() ||
                     x_u > FPBits::max_normal().uintval())) {
-    if (xbits.is_zero()) {
+    if (x == 0.0f) {
       fputil::set_errno_if_required(ERANGE);
       fputil::raise_except_if_required(FE_DIVBYZERO);
       return FPBits::inf(Sign::NEG).get_val();

libc/src/math/generic/logf.cpp

@@ -82,7 +82,7 @@ LLVM_LIBC_FUNCTION(float, logf, (float x)) {
     }
     // Subnormal inputs.
     if (LIBC_UNLIKELY(x_u < FPBits::min_normal().uintval())) {
-      if (x_u == 0) {
+      if (x == 0.0f) {
         // Return -inf and raise FE_DIVBYZERO
         fputil::set_errno_if_required(ERANGE);
         fputil::raise_except_if_required(FE_DIVBYZERO);