`d_mul_2exp, d_mul_2exp_inrange, d_mul_2exp_inrange2`

Synopsis#include <flint/double_extras.h>

double d_mul_2exp(double x, int i)source

double d_mul_2exp_inrange(double x, int i)source

double d_mul_2exp_inrange2(double x, int i)source

Return $x \cdot 2^i$ . The result is exact unless it overflows or is subnormal. d_mul_2exp accepts any $i$ and calls ldexp when $2^i$ is not a normal double. The other two are faster special cases with unchecked preconditions.

d_mul_2exp_inrange requires $-1022 \le i \le 1023$ . It builds the double $2^i$ from its bit pattern and performs one multiplication, so overflow, underflow and special values of $x$ behave as for an ordinary multiplication.

d_mul_2exp_inrange2 adds $i$ to the exponent field of $x$ with an integer addition. It additionally requires that $x$ and $x \cdot 2^i$ are normal doubles, in particular $x \ne 0$ ; otherwise the result is meaningless. The preconditions of both functions are checked only in builds configured with --enable-assert.

Cite this page

The FLINT team, “d_mul_2exp, d_mul_2exp_inrange, d_mul_2exp_inrange2 (double_extras.h),” FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev, 2026. https://flintlib.org/doc/double_extras/d_mul_2exp.html (generated 2026-11-02).

@misc{flint-doc-double-extras-d-mul-2exp,
  author       = {{The FLINT team}},
  title        = {{d\_mul\_2exp, d\_mul\_2exp\_inrange, d\_mul\_2exp\_inrange2 (double\_extras.h)}},
  howpublished = {FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev},
  year         = {2026},
  url          = {https://flintlib.org/doc/double_extras/d_mul_2exp.html},
  note         = {Generated 2026-11-02}
}

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