Average Error: 25.5 → 0.7
Time: 2.1m
Precision: 64
Internal Precision: 576
\[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
\[\frac{(\left(\frac{c}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) \cdot \left(\frac{b}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) + \left(\frac{-d}{\sqrt{c^2 + d^2}^*} \cdot a\right))_*}{\sqrt{c^2 + d^2}^*} + 0\]

Error

Bits error versus a

Bits error versus b

Bits error versus c

Bits error versus d

Target

Original25.5
Target0.5
Herbie0.7
\[\begin{array}{l} \mathbf{if}\;\left|d\right| \lt \left|c\right|:\\ \;\;\;\;\frac{b - a \cdot \frac{d}{c}}{c + d \cdot \frac{d}{c}}\\ \mathbf{else}:\\ \;\;\;\;\frac{\left(-a\right) + b \cdot \frac{c}{d}}{d + c \cdot \frac{c}{d}}\\ \end{array}\]

Derivation

  1. Initial program 25.5

    \[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}\]
  2. Using strategy rm
  3. Applied add-sqr-sqrt25.5

    \[\leadsto \frac{b \cdot c - a \cdot d}{\color{blue}{\sqrt{c \cdot c + d \cdot d} \cdot \sqrt{c \cdot c + d \cdot d}}}\]
  4. Applied *-un-lft-identity25.5

    \[\leadsto \frac{\color{blue}{1 \cdot \left(b \cdot c - a \cdot d\right)}}{\sqrt{c \cdot c + d \cdot d} \cdot \sqrt{c \cdot c + d \cdot d}}\]
  5. Applied times-frac25.6

    \[\leadsto \color{blue}{\frac{1}{\sqrt{c \cdot c + d \cdot d}} \cdot \frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}}\]
  6. Applied simplify25.6

    \[\leadsto \color{blue}{\frac{1}{\sqrt{c^2 + d^2}^*}} \cdot \frac{b \cdot c - a \cdot d}{\sqrt{c \cdot c + d \cdot d}}\]
  7. Applied simplify16.4

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \color{blue}{\frac{c \cdot b - a \cdot d}{\sqrt{c^2 + d^2}^*}}\]
  8. Using strategy rm
  9. Applied div-sub16.4

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \color{blue}{\left(\frac{c \cdot b}{\sqrt{c^2 + d^2}^*} - \frac{a \cdot d}{\sqrt{c^2 + d^2}^*}\right)}\]
  10. Using strategy rm
  11. Applied *-un-lft-identity16.4

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \left(\frac{c \cdot b}{\sqrt{c^2 + d^2}^*} - \frac{a \cdot d}{\color{blue}{1 \cdot \sqrt{c^2 + d^2}^*}}\right)\]
  12. Applied times-frac9.1

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \left(\frac{c \cdot b}{\sqrt{c^2 + d^2}^*} - \color{blue}{\frac{a}{1} \cdot \frac{d}{\sqrt{c^2 + d^2}^*}}\right)\]
  13. Applied add-sqr-sqrt9.1

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \left(\frac{c \cdot b}{\color{blue}{\sqrt{\sqrt{c^2 + d^2}^*} \cdot \sqrt{\sqrt{c^2 + d^2}^*}}} - \frac{a}{1} \cdot \frac{d}{\sqrt{c^2 + d^2}^*}\right)\]
  14. Applied times-frac0.8

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \left(\color{blue}{\frac{c}{\sqrt{\sqrt{c^2 + d^2}^*}} \cdot \frac{b}{\sqrt{\sqrt{c^2 + d^2}^*}}} - \frac{a}{1} \cdot \frac{d}{\sqrt{c^2 + d^2}^*}\right)\]
  15. Applied prod-diff0.8

    \[\leadsto \frac{1}{\sqrt{c^2 + d^2}^*} \cdot \color{blue}{\left((\left(\frac{c}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) \cdot \left(\frac{b}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) + \left(-\frac{d}{\sqrt{c^2 + d^2}^*} \cdot \frac{a}{1}\right))_* + (\left(-\frac{d}{\sqrt{c^2 + d^2}^*}\right) \cdot \left(\frac{a}{1}\right) + \left(\frac{d}{\sqrt{c^2 + d^2}^*} \cdot \frac{a}{1}\right))_*\right)}\]
  16. Applied distribute-lft-in0.8

    \[\leadsto \color{blue}{\frac{1}{\sqrt{c^2 + d^2}^*} \cdot (\left(\frac{c}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) \cdot \left(\frac{b}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) + \left(-\frac{d}{\sqrt{c^2 + d^2}^*} \cdot \frac{a}{1}\right))_* + \frac{1}{\sqrt{c^2 + d^2}^*} \cdot (\left(-\frac{d}{\sqrt{c^2 + d^2}^*}\right) \cdot \left(\frac{a}{1}\right) + \left(\frac{d}{\sqrt{c^2 + d^2}^*} \cdot \frac{a}{1}\right))_*}\]
  17. Applied simplify0.7

    \[\leadsto \color{blue}{\frac{(\left(\frac{c}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) \cdot \left(\frac{b}{\sqrt{\sqrt{c^2 + d^2}^*}}\right) + \left(\frac{-d}{\sqrt{c^2 + d^2}^*} \cdot a\right))_*}{\sqrt{c^2 + d^2}^*}} + \frac{1}{\sqrt{c^2 + d^2}^*} \cdot (\left(-\frac{d}{\sqrt{c^2 + d^2}^*}\right) \cdot \left(\frac{a}{1}\right) + \left(\frac{d}{\sqrt{c^2 + d^2}^*} \cdot \frac{a}{1}\right))_*\]
  18. Applied simplify0.7

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

Runtime

Time bar (total: 2.1m)Debug logProfile

herbie shell --seed 2018170 +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))))