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diff --git a/libc/src/__support/math/atanf_float.h b/libc/src/__support/math/atanf_float.h
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+//===-- Single-precision atanf float function -----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LIBC_SRC___SUPPORT_MATH_ATANF_FLOAT_H
+#define LIBC_SRC___SUPPORT_MATH_ATANF_FLOAT_H
+
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/double_double.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace atanf_internal {
+
+using fputil::FloatFloat;
+// atan(i/64) with i = 0..16, generated by Sollya with:
+// > for i from 0 to 16 do {
+// a = round(atan(i/16), SG, RN);
+// b = round(atan(i/16) - a, SG, RN);
+// print("{", b, ",", a, "},");
+// };
+static constexpr FloatFloat ATAN_I[17] = {
+ {0.0f, 0.0f},
+ {-0x1.1a6042p-30f, 0x1.ff55bcp-5f},
+ {-0x1.54f424p-30f, 0x1.fd5baap-4f},
+ {0x1.79cb6p-28f, 0x1.7b97b4p-3f},
+ {-0x1.b4dfc8p-29f, 0x1.f5b76p-3f},
+ {-0x1.1f0286p-27f, 0x1.362774p-2f},
+ {0x1.e4defp-30f, 0x1.6f6194p-2f},
+ {0x1.e611fep-29f, 0x1.a64eecp-2f},
+ {0x1.586ed4p-28f, 0x1.dac67p-2f},
+ {-0x1.6499e6p-26f, 0x1.0657eap-1f},
+ {0x1.7bdfd6p-26f, 0x1.1e00bap-1f},
+ {-0x1.98e422p-28f, 0x1.345f02p-1f},
+ {0x1.934f7p-28f, 0x1.4978fap-1f},
+ {0x1.c5a6c6p-27f, 0x1.5d5898p-1f},
+ {0x1.5e118cp-27f, 0x1.700a7cp-1f},
+ {-0x1.1d4eb6p-26f, 0x1.819d0cp-1f},
+ {-0x1.777a5cp-26f, 0x1.921fb6p-1f},
+};
+
+// 1 / (1 + (i/16)^2) with i = 0..16, generated by Sollya with:
+// > for i from 0 to 16 do {
+// a = round(1 / (1 + (i/16)^2), SG, RN);
+// print(a, ",");
+// };
+static constexpr float ATANF_REDUCED_ARG[17] = {
+ 0x1.0p0f, 0x1.fe01fep-1f, 0x1.f81f82p-1f, 0x1.ee9c8p-1f,
+ 0x1.e1e1e2p-1f, 0x1.d272cap-1f, 0x1.c0e07p-1f, 0x1.adbe88p-1f,
+ 0x1.99999ap-1f, 0x1.84f00cp-1f, 0x1.702e06p-1f, 0x1.5babccp-1f,
+ 0x1.47ae14p-1f, 0x1.34679ap-1f, 0x1.21fb78p-1f, 0x1.107fbcp-1f,
+ 0x1p-1f,
+};
+
+// Approximating atan( u / (1 + u * k/16) )
+// atan( u / (1 + u * k/16) ) / u ~ 1 - k/16 * u + (k^2/256 - 1/3) * u^2 +
+// + (k/16 - (k/16)^3) * u^3 + O(u^4)
+LIBC_INLINE static float atanf_eval(float u, float k_over_16) {
+ // (k/16)^2
+ float c2 = k_over_16 * k_over_16;
+ // -(k/16)^3
+ float c3 = fputil::multiply_add(-k_over_16, c2, k_over_16);
+ float u2 = u * u;
+ // (k^2/256 - 1/3) + u * (k/16 - (k/16)^3)
+ float a0 = fputil::multiply_add(c3, u, c2 - 0x1.555556p-2f);
+ // -k/16 + u*(k^2/256 - 1/3) + u^2 * (k/16 - (k/16)^3)
+ float a1 = fputil::multiply_add(u, a0, -k_over_16);
+ // u - u^2 * k/16 + u^3 * ((k^2/256 - 1/3) + u^4 * (k/16 - (k/16)^3))
+ return fputil::multiply_add(u2, a1, u);
+}
+
+} // namespace atanf_internal
+
+// There are several range reduction steps we can take for atan2(y, x) as
+// follow:
+
+LIBC_INLINE static float atanf(float x) {
+ using namespace atanf_internal;
+ using FPBits = typename fputil::FPBits<float>;
+ using FPBits = typename fputil::FPBits<float>;
+
+ constexpr float SIGN[2] = {1.0f, -1.0f};
+ constexpr FloatFloat PI_OVER_2 = {-0x1.777a5cp-25f, 0x1.921fb6p0f};
+
+ FPBits x_bits(x);
+ Sign s = x_bits.sign();
+ float sign = SIGN[s.is_neg()];
+ uint32_t x_abs = x_bits.uintval() & 0x7fff'ffffU;
+
+ // x is inf or nan, |x| <= 2^-11 or |x|= > 2^11.
+ if (LIBC_UNLIKELY(x_abs <= 0x3a00'0000U || x_abs >= 0x4500'0000U)) {
+ if (LIBC_UNLIKELY(x_bits.is_inf()))
+ return sign * PI_OVER_2.hi;
+ // atan(NaN) = NaN
+ if (LIBC_UNLIKELY(x_bits.is_nan())) {
+ if (x_bits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+
+ return x;
+ }
+ // |x| >= 2^11:
+ // atan(x) = sign(x) * pi/2 - atan(1/x)
+ // ~ sign(x) * pi/2 - 1/x
+ if (LIBC_UNLIKELY(x_abs >= 0x4200'0000))
+ return fputil::multiply_add(sign, PI_OVER_2.hi, -1.0f / x);
+ // x <= 2^-11:
+ // atan(x) ~ x
+ return x;
+ }
+
+ // Range reduction steps:
+ // 1) atan(x) = sign(x) * atan(|x|)
+ // 2) If |x| > 1, atan(|x|) = pi/2 - atan(1/|x|)
+ // 3) For 1/16 < |x| < 1 + 1/32, we find k such that: | |x| - k/16 | <= 1/32.
+ // Let y = |x| - k/16, then using the angle summation formula, we have:
+ // atan(|x|) = atan(k/16) + atan( (|x| - k/16) / (1 + |x| * k/16) )
+ // = atan(k/16) + atan( y / (1 + (y + k/16) * k/16 )
+ // = atan(k/16) + atan( y / ((1 + k^2/256) + y * k/16) )
+ // 4) Let u = y / (1 + k^2/256), then we can rewritten the above as:
+ // atan(|x|) = atan(k/16) + atan( u / (1 + u * k/16) )
+ // ~ atan(k/16) + (u - k/16 * u^2 + (k^2/256 - 1/3) * u^3 +
+ // + (k/16 - (k/16)^3) * u^4) + O(u^5)
+ float x_a = cpp::bit_cast<float>(x_abs);
+ // |x| > 1 + 1/32, we need to invert x, so we will perform the division in
+ // float-float.
+ if (x_abs > 0x3f84'0000U)
+ x_a = 1.0f / x_a;
+ // Perform range reduction.
+ // k = nearestint(x * 16)
+ float k_f = fputil::nearest_integer(x_a * 0x1.0p4f);
+ unsigned idx = static_cast<unsigned>(k_f);
+ float k_over_16 = k_f * 0x1.0p-4f;
+ float y = x_a - k_over_16;
+ // u = (x - k/16) / (1 + (k/16)^2)
+ float u = y * ATANF_REDUCED_ARG[idx];
+
+ // atan(x) = sign(x) * atan(|x|)
+ // = sign(x) * (atan(k/16) + atan(|))
+ // p ~ atan(u)
+ float p = atanf_eval(u, k_over_16);
+ // |x| > 1 + 1/32: q ~ (pi/2 - atan(1/|x|))
+ // |x| <= 1 + 1/32: q ~ atan(|x|)
+ float q = (p + ATAN_I[idx].lo) + ATAN_I[idx].hi;
+ if (x_abs > 0x3f84'0000U)
+ q = PI_OVER_2.hi + (PI_OVER_2.lo - q);
+ // |x| > 1 + 1/32: sign(x) * (pi/2 - atan(1/|x|))
+ // |x| <= 1 + 1/32: sign(x) * atan(|x|)
+ return sign * q;
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_SRC___SUPPORT_MATH_ATANF_FLOAT_H
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