Exception for 2isqrt (example 3.6)

Specification

\[x > 1 \land x < 10^{+308}\]

Math

\[\begin{array}{l} \\ \frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}} \end{array} \]

FPCore

(FPCore (x) :precision binary64 (- (/ 1.0 (sqrt x)) (/ 1.0 (sqrt (+ x 1.0)))))

C

double code(double x) {
	return (1.0 / sqrt(x)) - (1.0 / sqrt((x + 1.0)));
}

Fortran

real(8) function code(x)
    real(8), intent (in) :: x
    code = (1.0d0 / sqrt(x)) - (1.0d0 / sqrt((x + 1.0d0)))
end function

Java

public static double code(double x) {
	return (1.0 / Math.sqrt(x)) - (1.0 / Math.sqrt((x + 1.0)));
}

Python

def code(x):
	return (1.0 / math.sqrt(x)) - (1.0 / math.sqrt((x + 1.0)))

Julia

function code(x)
	return Float64(Float64(1.0 / sqrt(x)) - Float64(1.0 / sqrt(Float64(x + 1.0))))
end

MATLAB

function tmp = code(x)
	tmp = (1.0 / sqrt(x)) - (1.0 / sqrt((x + 1.0)));
end

Wolfram

code[x_] := N[(N[(1.0 / N[Sqrt[x], $MachinePrecision]), $MachinePrecision] - N[(1.0 / N[Sqrt[N[(x + 1.0), $MachinePrecision]], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]

Reproduce

herbie shell --seed 2024039 
(FPCore (x)
  :name "2isqrt (example 3.6)"
  :precision binary64
  :pre (and (> x 1.0) (< x 1e+308))

  :herbie-target
  (/ 1.0 (+ (* (+ x 1.0) (sqrt x)) (* x (sqrt (+ x 1.0)))))

  (- (/ 1.0 (sqrt x)) (/ 1.0 (sqrt (+ x 1.0)))))

Please file a bug report with this information.

Backtrace

member: not a proper list in: 1		L	C
gather-multiplicative-terms	/home/nightlies/herbie/sound-rules/src/core/reduce.rkt	125	0
simplify-node*	/home/nightlies/herbie/sound-rules/src/core/reduce.rkt	84	0
hash-ref!	/usr/local/racket/collects/racket/private/more-scheme.rkt	377	2
hash-ref!	/usr/local/racket/collects/racket/private/more-scheme.rkt	377	2
loop	.../private/map.rkt	40	19
f19	.../match/compiler.rkt	559	40
hash-ref!	/usr/local/racket/collects/racket/private/more-scheme.rkt	377	2
approximate	/home/nightlies/herbie/sound-rules/src/core/taylor.rkt	7	0
taylor-expr	/home/nightlies/herbie/sound-rules/src/patch.rkt	89	0
taylor-alt	/home/nightlies/herbie/sound-rules/src/patch.rkt	96	0
gen-series!	/home/nightlies/herbie/sound-rules/src/patch.rkt	109	0
patch-table-run	/home/nightlies/herbie/sound-rules/src/patch.rkt	257	0
(unnamed)	/usr/local/racket/collects/racket/contract/private/arrow-val-first.rkt	486	18
run-iter!	/home/nightlies/herbie/sound-rules/src/mainloop.rkt	288	0
mutate!	/home/nightlies/herbie/sound-rules/src/mainloop.rkt	340	0
run-improve!	/home/nightlies/herbie/sound-rules/src/mainloop.rkt	326	0
get-alternatives/report	/home/nightlies/herbie/sound-rules/src/sandbox.rkt	169	0
(unnamed)	/home/nightlies/herbie/sound-rules/src/sandbox.rkt	262	6
(unnamed)	/usr/local/racket/share/pkgs/profile-lib/main.rkt	40	10
profile-thunk	/usr/local/racket/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/usr/local/racket/collects/racket/engine.rkt	42	24