| //===-- Single-precision sin 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 |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "src/math/sinf.h" |
| #include "common_constants.h" |
| #include "src/__support/FPUtil/BasicOperations.h" |
| #include "src/__support/FPUtil/FEnvImpl.h" |
| #include "src/__support/FPUtil/FPBits.h" |
| #include "src/__support/FPUtil/PolyEval.h" |
| #include "src/__support/FPUtil/except_value_utils.h" |
| #include "src/__support/FPUtil/multiply_add.h" |
| #include "src/__support/common.h" |
| |
| #include <errno.h> |
| |
| #if defined(LIBC_TARGET_HAS_FMA) |
| #include "range_reduction_fma.h" |
| // using namespace __llvm_libc::fma; |
| using __llvm_libc::fma::FAST_PASS_BOUND; |
| using __llvm_libc::fma::large_range_reduction; |
| using __llvm_libc::fma::N_EXCEPTS; |
| using __llvm_libc::fma::SinfExcepts; |
| using __llvm_libc::fma::small_range_reduction; |
| #else |
| #include "range_reduction.h" |
| // using namespace __llvm_libc::generic; |
| using __llvm_libc::generic::FAST_PASS_BOUND; |
| using __llvm_libc::generic::large_range_reduction; |
| using __llvm_libc::generic::N_EXCEPTS; |
| using __llvm_libc::generic::SinfExcepts; |
| using __llvm_libc::generic::small_range_reduction; |
| #endif |
| |
| namespace __llvm_libc { |
| |
| LLVM_LIBC_FUNCTION(float, sinf, (float x)) { |
| using FPBits = typename fputil::FPBits<float>; |
| FPBits xbits(x); |
| |
| uint32_t x_u = xbits.uintval(); |
| uint32_t x_abs = x_u & 0x7fff'ffffU; |
| double xd = static_cast<double>(x); |
| |
| // Range reduction: |
| // For |x| > pi/16, we perform range reduction as follows: |
| // Find k and y such that: |
| // x = (k + y) * pi/16 |
| // k is an integer |
| // |y| < 0.5 |
| // For small range (|x| < 2^46 when FMA instructions are available, 2^22 |
| // otherwise), this is done by performing: |
| // k = round(x * 16/pi) |
| // y = x * 16/pi - k |
| // For large range, we will omit all the higher parts of 16/pi such that the |
| // least significant bits of their full products with x are larger than 31, |
| // since sin((k + y + 32*i) * pi/16) = sin(x + i * 2pi) = sin(x). |
| // |
| // When FMA instructions are not available, we store the digits of 16/pi in |
| // chunks of 28-bit precision. This will make sure that the products: |
| // x * SIXTEEN_OVER_PI_28[i] are all exact. |
| // When FMA instructions are available, we simply store the digits of 16/pi in |
| // chunks of doubles (53-bit of precision). |
| // So when multiplying by the largest values of single precision, the |
| // resulting output should be correct up to 2^(-208 + 128) ~ 2^-80. By the |
| // worst-case analysis of range reduction, |y| >= 2^-38, so this should give |
| // us more than 40 bits of accuracy. For the worst-case estimation of range |
| // reduction, see for instances: |
| // Elementary Functions by J-M. Muller, Chapter 11, |
| // Handbook of Floating-Point Arithmetic by J-M. Muller et. al., |
| // Chapter 10.2. |
| // |
| // Once k and y are computed, we then deduce the answer by the sine of sum |
| // formula: |
| // sin(x) = sin((k + y)*pi/16) |
| // = sin(y*pi/16) * cos(k*pi/16) + cos(y*pi/16) * sin(k*pi/16) |
| // The values of sin(k*pi/16) and cos(k*pi/16) for k = 0..31 are precomputed |
| // and stored using a vector of 32 doubles. Sin(y*pi/16) and cos(y*pi/16) are |
| // computed using degree-7 and degree-8 minimax polynomials generated by |
| // Sollya respectively. |
| |
| // |x| <= pi/16 |
| if (unlikely(x_abs <= 0x3e49'0fdbU)) { |
| |
| // |x| < 0x1.d12ed2p-12f |
| if (unlikely(x_abs < 0x39e8'9769U)) { |
| if (unlikely(x_abs == 0U)) { |
| // For signed zeros. |
| return x; |
| } |
| // When |x| < 2^-12, the relative error of the approximation sin(x) ~ x |
| // is: |
| // |sin(x) - x| / |sin(x)| < |x^3| / (6|x|) |
| // = x^2 / 6 |
| // < 2^-25 |
| // < epsilon(1)/2. |
| // So the correctly rounded values of sin(x) are: |
| // = x - sign(x)*eps(x) if rounding mode = FE_TOWARDZERO, |
| // or (rounding mode = FE_UPWARD and x is |
| // negative), |
| // = x otherwise. |
| // To simplify the rounding decision and make it more efficient, we use |
| // fma(x, -2^-25, x) instead. |
| // An exhaustive test shows that this formula work correctly for all |
| // rounding modes up to |x| < 0x1.c555dep-11f. |
| // Note: to use the formula x - 2^-25*x to decide the correct rounding, we |
| // do need fma(x, -2^-25, x) to prevent underflow caused by -2^-25*x when |
| // |x| < 2^-125. For targets without FMA instructions, we simply use |
| // double for intermediate results as it is more efficient than using an |
| // emulated version of FMA. |
| #if defined(LIBC_TARGET_HAS_FMA) |
| return fputil::multiply_add(x, -0x1.0p-25f, x); |
| #else |
| return static_cast<float>(fputil::multiply_add(xd, -0x1.0p-25, xd)); |
| #endif // LIBC_TARGET_HAS_FMA |
| } |
| |
| // |x| < pi/16. |
| double xsq = xd * xd; |
| |
| // Degree-9 polynomial approximation: |
| // sin(x) ~ x + a_3 x^3 + a_5 x^5 + a_7 x^7 + a_9 x^9 |
| // = x (1 + a_3 x^2 + ... + a_9 x^8) |
| // = x * P(x^2) |
| // generated by Sollya with the following commands: |
| // > display = hexadecimal; |
| // > Q = fpminimax(sin(x)/x, [|0, 2, 4, 6, 8|], [|1, D...|], [0, pi/16]); |
| double result = |
| fputil::polyeval(xsq, 1.0, -0x1.55555555554c6p-3, 0x1.1111111085e65p-7, |
| -0x1.a019f70fb4d4fp-13, 0x1.718d179815e74p-19); |
| return xd * result; |
| } |
| |
| using ExceptChecker = typename fputil::ExceptionChecker<float, N_EXCEPTS>; |
| { |
| float result; |
| if (ExceptChecker::check_odd_func(SinfExcepts, x_abs, xbits.get_sign(), |
| result)) |
| return result; |
| } |
| |
| int k; |
| double y; |
| |
| if (likely(x_abs < FAST_PASS_BOUND)) { |
| k = small_range_reduction(xd, y); |
| } else { |
| // x is inf or nan. |
| if (unlikely(x_abs >= 0x7f80'0000U)) { |
| if (x_abs == 0x7f80'0000U) { |
| errno = EDOM; |
| fputil::set_except(FE_INVALID); |
| } |
| return x + |
| FPBits::build_nan(1 << (fputil::MantissaWidth<float>::VALUE - 1)); |
| } |
| |
| k = large_range_reduction(xd, xbits.get_exponent(), y); |
| } |
| |
| // After range reduction, k = round(x * 16 / pi) and y = (x * 16 / pi) - k. |
| // So k is an integer and -0.5 <= y <= 0.5. |
| // Then sin(x) = sin((k + y)*pi/16) |
| // = sin(y*pi/16) * cos(k*pi/16) + cos(y*pi/16) * sin(k*pi/16) |
| |
| double ysq = y * y; |
| |
| // Degree-6 minimax even polynomial for sin(y*pi/16)/y generated by Sollya |
| // with: |
| // > Q = fpminimax(sin(y*pi/16)/y, [|0, 2, 4, 6|], [|D...|], [0, 0.5]); |
| double sin_y = |
| fputil::polyeval(ysq, 0x1.921fb54442d17p-3, -0x1.4abbce6256adp-10, |
| 0x1.466bc5a5ac6b3p-19, -0x1.32bdcb4207562p-29); |
| // Degree-8 minimax even polynomial for cos(y*pi/16) generated by Sollya with: |
| // > P = fpminimax(cos(x*pi/16), [|0, 2, 4, 6, 8|], [|1, D...|], [0, 0.5]); |
| // Note that cosm1_y = cos(y*pi/16) - 1. |
| double cosm1_y = |
| ysq * fputil::polyeval(ysq, -0x1.3bd3cc9be45dcp-6, 0x1.03c1f081b08ap-14, |
| -0x1.55d3c6fb0fb6ep-24, 0x1.e1d3d60f58873p-35); |
| |
| double sin_k = SIN_K_PI_OVER_16[k & 31]; |
| // cos(k * pi/16) = sin(k * pi/16 + pi/2) = sin((k + 8) * pi/16). |
| // cos_k = y * cos(k * pi/16) |
| double cos_k = y * SIN_K_PI_OVER_16[(k + 8) & 31]; |
| |
| // Combine the results with the sine of sum formula: |
| // sin(x) = sin((k + y)*pi/16) |
| // = sin(y*pi/16) * cos(k*pi/16) + cos(y*pi/16) * sin(k*pi/16) |
| // = sin_y * cos_k + (1 + cosm1_y) * sin_k |
| // = sin_y * cos_k + (cosm1_y * sin_k + sin_k) |
| return fputil::multiply_add(sin_y, cos_k, |
| fputil::multiply_add(cosm1_y, sin_k, sin_k)); |
| } |
| |
| } // namespace __llvm_libc |