`radix_rsqrt_approx_basecase, radix_rsqrt_approx`

Synopsis#include <flint/radix.h>

void radix_rsqrt_approx_basecase(nn_ptr q, nn_srcptr a, slong an, slong n, const radix_t radix)source

void radix_rsqrt_approx(nn_ptr q, nn_srcptr a, slong an, slong n, const radix_t radix)source

Given $(a, \mathit{an})$ read as a fixed-point number $a \in [B^{-2}, 1)$ with $\mathit{an}$ fraction limbs (one of the top two limbs nonzero), set $(q, n + 2)$ to an approximation of $1/\sqrt a \in (1, B]$ with $n$ fraction limbs and two integral limbs, with absolute error less than $4 B^{-n}/\sqrt a$ . The range of $a$ is wider than for radix_inv_approx so that inputs with an odd number of limbs can be handled, the scale factor $B^{1/2}$ not being a limb shift.

Cite this page

The FLINT team, “radix_rsqrt_approx_basecase, radix_rsqrt_approx (radix.h),” FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev, 2026. https://flintlib.org/doc/radix/radix_rsqrt_approx_basecase.html (generated 2026-11-02).

@misc{flint-doc-radix-radix-rsqrt-approx-basecase,
  author       = {{The FLINT team}},
  title        = {{radix\_rsqrt\_approx\_basecase, radix\_rsqrt\_approx (radix.h)}},
  howpublished = {FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev},
  year         = {2026},
  url          = {https://flintlib.org/doc/radix/radix_rsqrt_approx_basecase.html},
  note         = {Generated 2026-11-02}
}

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