src/algorithms/ilogb.rs

   1 use crate::{
   2     f16::F16,
   3     ieee754::FloatEncoding,
   4     traits::{Compare, Context, ConvertTo, Float, Select},
   5 };
   6
   7 macro_rules! impl_ilogb {
   8     (
   9         #[prim = $prim:ident]
  10         #[prim_signed_bits = $prim_signed_bits:ident]
  11         #[ilogb = $ilogb:ident]
  12         #[nan = $NAN_RESULT:ident]
  13         #[overflow = $OVERFLOW_RESULT:ident]
  14         #[underflow = $UNDERFLOW_RESULT:ident]
  15         fn $ilogb_extended:ident($vector_float:ident, $scalar_signed_bits:ident) -> $vector_signed_bits:ident;
  16     ) => {
  17         pub const $NAN_RESULT: $prim_signed_bits = $prim_signed_bits::MIN + 1;
  18         pub const $OVERFLOW_RESULT: $prim_signed_bits = $prim_signed_bits::MAX;
  19         pub const $UNDERFLOW_RESULT: $prim_signed_bits = $prim_signed_bits::MIN;
  20
  21         pub fn $ilogb_extended<Ctx: Context>(
  22             ctx: Ctx,
  23             arg: Ctx::$vector_float,
  24             nan_result: Ctx::$scalar_signed_bits,
  25             overflow_result: Ctx::$scalar_signed_bits,
  26             underflow_result: Ctx::$scalar_signed_bits,
  27         ) -> Ctx::$vector_signed_bits {
  28             let is_finite = arg.is_finite();
  29             let is_zero_subnormal = arg.is_zero_or_subnormal();
  30             let is_nan = arg.is_nan();
  31             let inf_nan_result: Ctx::$vector_signed_bits =
  32                 is_nan.select(nan_result.into(), overflow_result.into());
  33             let scale_factor: $prim = (1u64 << $prim::MANTISSA_FIELD_WIDTH).to();
  34             let scaled = arg * ctx.make(scale_factor);
  35             let scaled_exponent = scaled.extract_exponent_unbiased();
  36             let exponent = arg.extract_exponent_unbiased();
  37             let normal_inf_nan_result = is_finite.select(exponent, inf_nan_result);
  38             let is_zero = arg.eq(ctx.make($prim::from(0u8)));
  39             let zero_subnormal_result = is_zero.select(
  40                 underflow_result.into(),
  41                 scaled_exponent - ctx.make($prim::MANTISSA_FIELD_WIDTH.to()),
  42             );
  43             is_zero_subnormal.select(zero_subnormal_result, normal_inf_nan_result)
  44         }
  45
  46         pub fn $ilogb<Ctx: Context>(ctx: Ctx, arg: Ctx::$vector_float) -> Ctx::$vector_signed_bits {
  47             $ilogb_extended(
  48                 ctx,
  49                 arg,
  50                 ctx.make($NAN_RESULT),
  51                 ctx.make($OVERFLOW_RESULT),
  52                 ctx.make($UNDERFLOW_RESULT),
  53             )
  54         }
  55     };
  56 }
  57
  58 impl_ilogb! {
  59     #[prim = F16]
  60     #[prim_signed_bits = i16]
  61     #[ilogb = ilogb_f16]
  62     #[nan = ILOGB_NAN_RESULT_F16]
  63     #[overflow = ILOGB_OVERFLOW_RESULT_F16]
  64     #[underflow = ILOGB_UNDERFLOW_RESULT_F16]
  65     fn ilogb_f16_extended(VecF16, I16) -> VecI16;
  66 }
  67
  68 impl_ilogb! {
  69     #[prim = f32]
  70     #[prim_signed_bits = i32]
  71     #[ilogb = ilogb_f32]
  72     #[nan = ILOGB_NAN_RESULT_F32]
  73     #[overflow = ILOGB_OVERFLOW_RESULT_F32]
  74     #[underflow = ILOGB_UNDERFLOW_RESULT_F32]
  75     fn ilogb_f32_extended(VecF32, I32) -> VecI32;
  76 }
  77
  78 impl_ilogb! {
  79     #[prim = f64]
  80     #[prim_signed_bits = i64]
  81     #[ilogb = ilogb_f64]
  82     #[nan = ILOGB_NAN_RESULT_F64]
  83     #[overflow = ILOGB_OVERFLOW_RESULT_F64]
  84     #[underflow = ILOGB_UNDERFLOW_RESULT_F64]
  85     fn ilogb_f64_extended(VecF64, I64) -> VecI64;
  86 }
  87
  88 #[cfg(test)]
  89 mod tests {
  90     use super::*;
  91     use crate::scalar::{Scalar, Value};
  92
  93     #[test]
  94     #[cfg_attr(
  95         not(feature = "f16"),
  96         should_panic(expected = "f16 feature is not enabled")
  97     )]
  98     fn test_ilogb_f16() {
  99         fn ilogb(arg: f32) -> i16 {
 100             let arg: F16 = arg.to();
 101             ilogb_f16(Scalar, Value(arg)).0
 102         }
 103         assert_eq!(ilogb(0.), ILOGB_UNDERFLOW_RESULT_F16);
 104         assert_eq!(ilogb(1.), 0);
 105         assert_eq!(ilogb(2.), 1);
 106         assert_eq!(ilogb(3.), 1);
 107         assert_eq!(ilogb(3.998), 1);
 108         assert_eq!(ilogb(0.5), -1);
 109         assert_eq!(ilogb(0.5f32.powi(20)), -20);
 110         assert_eq!(ilogb(f32::INFINITY), ILOGB_OVERFLOW_RESULT_F16);
 111         assert_eq!(ilogb(f32::NAN), ILOGB_NAN_RESULT_F16);
 112     }
 113
 114     #[test]
 115     fn test_ilogb_f32() {
 116         fn ilogb(arg: f32) -> i32 {
 117             ilogb_f32(Scalar, Value(arg)).0
 118         }
 119         assert_eq!(ilogb(0f32), ILOGB_UNDERFLOW_RESULT_F32);
 120         assert_eq!(ilogb(1f32), 0);
 121         assert_eq!(ilogb(2f32), 1);
 122         assert_eq!(ilogb(3f32), 1);
 123         assert_eq!(ilogb(3.99999f32), 1);
 124         assert_eq!(ilogb(0.5f32), -1);
 125         assert_eq!(ilogb(0.5f32.powi(130)), -130);
 126         assert_eq!(ilogb(f32::INFINITY), ILOGB_OVERFLOW_RESULT_F32);
 127         assert_eq!(ilogb(f32::NAN), ILOGB_NAN_RESULT_F32);
 128     }
 129
 130     #[test]
 131     fn test_ilogb_f64() {
 132         fn ilogb(arg: f64) -> i64 {
 133             ilogb_f64(Scalar, Value(arg)).0
 134         }
 135         assert_eq!(ilogb(0f64), ILOGB_UNDERFLOW_RESULT_F64);
 136         assert_eq!(ilogb(1f64), 0);
 137         assert_eq!(ilogb(2f64), 1);
 138         assert_eq!(ilogb(3f64), 1);
 139         assert_eq!(ilogb(3.99999f64), 1);
 140         assert_eq!(ilogb(0.5f64), -1);
 141         assert_eq!(ilogb(0.5f64.powi(1030)), -1030);
 142         assert_eq!(ilogb(f64::INFINITY), ILOGB_OVERFLOW_RESULT_F64);
 143         assert_eq!(ilogb(f64::NAN), ILOGB_NAN_RESULT_F64);
 144     }
 145 }