Average Error: 26.5 → 13.6
Time: 4.0m
Precision: 64
Internal Precision: 128
\[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
\[\begin{array}{l} \mathbf{if}\;c \le -1.586349612154054 \cdot 10^{+218}:\\ \;\;\;\;\frac{-b}{\sqrt{c^2 + d^2}^*}\\ \mathbf{elif}\;c \le 6.788602011952196 \cdot 10^{+137}:\\ \;\;\;\;\frac{\left(b \cdot c - d \cdot a\right) \cdot \frac{1}{\sqrt{c^2 + d^2}^*}}{\sqrt{c^2 + d^2}^*}\\ \mathbf{else}:\\ \;\;\;\;\frac{b}{\sqrt{c^2 + d^2}^*}\\ \end{array}\]

Error

Bits error versus a

Bits error versus b

Bits error versus c

Bits error versus d

Target

Original26.5
Target0.4
Herbie13.6
\[\begin{array}{l} \mathbf{if}\;\left|d\right| \lt \left|c\right|:\\ \;\;\;\;\frac{b - a \cdot \frac{d}{c}}{c + d \cdot \frac{d}{c}}\\ \mathbf{else}:\\ \;\;\;\;\frac{\left(-a\right) + b \cdot \frac{c}{d}}{d + c \cdot \frac{c}{d}}\\ \end{array}\]

Derivation

  1. Split input into 3 regimes
  2. if c < -1.586349612154054e+218

    1. Initial program 43.7

      \[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
    2. Using strategy rm
    3. Applied add-sqr-sqrt43.7

      \[\leadsto \frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{c \cdot c + d \cdot d} \cdot \sqrt{c \cdot c + d \cdot d}}}\]
    4. Applied associate-/r*43.7

      \[\leadsto \color{blue}{\frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + d \cdot d}}}\]
    5. Using strategy rm
    6. Applied *-commutative43.7

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + \color{blue}{d \cdot d}}}\]
    7. Applied add-sqr-sqrt62.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot \color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    8. Applied add-sqr-sqrt62.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} \cdot \left(\sqrt{c} \cdot \sqrt{c}\right) + d \cdot d}}\]
    9. Applied unswap-sqr62.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right) \cdot \left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    10. Applied hypot-def62.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\color{blue}{\sqrt{\left(\sqrt{c} \cdot \sqrt{c}\right)^2 + d^2}^*}}\]
    11. Simplified43.7

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{c}^2 + d^2}^*}\]
    12. Taylor expanded around -inf 11.1

      \[\leadsto \frac{\color{blue}{-1 \cdot b}}{\sqrt{c^2 + d^2}^*}\]
    13. Simplified11.1

      \[\leadsto \frac{\color{blue}{-b}}{\sqrt{c^2 + d^2}^*}\]

    if -1.586349612154054e+218 < c < 6.788602011952196e+137

    1. Initial program 21.4

      \[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
    2. Using strategy rm
    3. Applied add-sqr-sqrt21.4

      \[\leadsto \frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{c \cdot c + d \cdot d} \cdot \sqrt{c \cdot c + d \cdot d}}}\]
    4. Applied associate-/r*21.3

      \[\leadsto \color{blue}{\frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + d \cdot d}}}\]
    5. Using strategy rm
    6. Applied *-commutative21.3

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + \color{blue}{d \cdot d}}}\]
    7. Applied add-sqr-sqrt42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot \color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    8. Applied add-sqr-sqrt42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} \cdot \left(\sqrt{c} \cdot \sqrt{c}\right) + d \cdot d}}\]
    9. Applied unswap-sqr42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right) \cdot \left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    10. Applied hypot-def42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\color{blue}{\sqrt{\left(\sqrt{c} \cdot \sqrt{c}\right)^2 + d^2}^*}}\]
    11. Simplified21.3

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{c}^2 + d^2}^*}\]
    12. Using strategy rm
    13. Applied *-commutative21.3

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + \color{blue}{d \cdot d}}}}{\sqrt{c^2 + d^2}^*}\]
    14. Applied add-sqr-sqrt42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot \color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    15. Applied add-sqr-sqrt42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} \cdot \left(\sqrt{c} \cdot \sqrt{c}\right) + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    16. Applied swap-sqr42.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right) \cdot \left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    17. Applied hypot-def39.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{\left(\sqrt{c} \cdot \sqrt{c}\right)^2 + d^2}^*}}}{\sqrt{c^2 + d^2}^*}\]
    18. Simplified13.3

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{c}^2 + d^2}^*}}{\sqrt{c^2 + d^2}^*}\]
    19. Using strategy rm
    20. Applied div-inv13.4

      \[\leadsto \frac{\color{blue}{\left(b \cdot c - a \cdot d\right) \cdot \frac{1}{\sqrt{c^2 + d^2}^*}}}{\sqrt{c^2 + d^2}^*}\]

    if 6.788602011952196e+137 < c

    1. Initial program 44.0

      \[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
    2. Using strategy rm
    3. Applied add-sqr-sqrt44.0

      \[\leadsto \frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{c \cdot c + d \cdot d} \cdot \sqrt{c \cdot c + d \cdot d}}}\]
    4. Applied associate-/r*44.0

      \[\leadsto \color{blue}{\frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + d \cdot d}}}\]
    5. Using strategy rm
    6. Applied *-commutative44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot c + \color{blue}{d \cdot d}}}\]
    7. Applied add-sqr-sqrt44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{c \cdot \color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    8. Applied add-sqr-sqrt44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} \cdot \left(\sqrt{c} \cdot \sqrt{c}\right) + d \cdot d}}\]
    9. Applied unswap-sqr44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right) \cdot \left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}\]
    10. Applied hypot-def44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\color{blue}{\sqrt{\left(\sqrt{c} \cdot \sqrt{c}\right)^2 + d^2}^*}}\]
    11. Simplified44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}{\sqrt{\color{blue}{c}^2 + d^2}^*}\]
    12. Using strategy rm
    13. Applied *-commutative44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + \color{blue}{d \cdot d}}}}{\sqrt{c^2 + d^2}^*}\]
    14. Applied add-sqr-sqrt44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{c \cdot \color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    15. Applied add-sqr-sqrt44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right)} \cdot \left(\sqrt{c} \cdot \sqrt{c}\right) + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    16. Applied swap-sqr44.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{\left(\sqrt{c} \cdot \sqrt{c}\right) \cdot \left(\sqrt{c} \cdot \sqrt{c}\right)} + d \cdot d}}}{\sqrt{c^2 + d^2}^*}\]
    17. Applied hypot-def28.0

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{\left(\sqrt{c} \cdot \sqrt{c}\right)^2 + d^2}^*}}}{\sqrt{c^2 + d^2}^*}\]
    18. Simplified27.9

      \[\leadsto \frac{\frac{b \cdot c - a \cdot d}{\sqrt{\color{blue}{c}^2 + d^2}^*}}{\sqrt{c^2 + d^2}^*}\]
    19. Taylor expanded around inf 16.1

      \[\leadsto \frac{\color{blue}{b}}{\sqrt{c^2 + d^2}^*}\]
  3. Recombined 3 regimes into one program.
  4. Final simplification13.6

    \[\leadsto \begin{array}{l} \mathbf{if}\;c \le -1.586349612154054 \cdot 10^{+218}:\\ \;\;\;\;\frac{-b}{\sqrt{c^2 + d^2}^*}\\ \mathbf{elif}\;c \le 6.788602011952196 \cdot 10^{+137}:\\ \;\;\;\;\frac{\left(b \cdot c - d \cdot a\right) \cdot \frac{1}{\sqrt{c^2 + d^2}^*}}{\sqrt{c^2 + d^2}^*}\\ \mathbf{else}:\\ \;\;\;\;\frac{b}{\sqrt{c^2 + d^2}^*}\\ \end{array}\]

Reproduce

herbie shell --seed 2019088 +o rules:numerics
(FPCore (a b c d)
  :name "Complex division, imag part"

  :herbie-target
  (if (< (fabs d) (fabs c)) (/ (- b (* a (/ d c))) (+ c (* d (/ d c)))) (/ (+ (- a) (* b (/ c d))) (+ d (* c (/ c d)))))

  (/ (- (* b c) (* a d)) (+ (* c c) (* d d))))