FLINT3.7.0-dev
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sd_fft_ctx_trunc_index

Synopsis#include <flint/fft_small.h>
ulong sd_fft_ctx_trunc_index(ulong L, ulong i)source

The position of f(w_i) in the output of a forward transform of length 2^L: i itself for L < 4, and otherwise i with the two 2-bit fields of its low four bits exchanged, which transposes each group of 16 values as a 4 \times 4 matrix.

Cite this page

The FLINT team, “sd_fft_ctx_trunc_index (fft_small.h),” FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev, 2026. https://flintlib.org/doc/fft_small/sd_fft_ctx_trunc_index.html (generated 2026-10-20).