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Reduce multiplication depth in _gr_poly_compose_axnc #2483

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Reduce multiplication depth in _gr_poly_compose_axnc #2483

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00ddb74
Reduce multiplication depth in _gr_poly_compose_axnc
user202729 Nov 9, 2025
5e1f9e4
Alternative algorithm
user202729 Nov 10, 2025
9e67366
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user202729 Nov 11, 2025
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31 changes: 20 additions & 11 deletions src/gr_generic/generic.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2612,23 +2612,32 @@ gr_generic_vec_dot_fmpz(gr_ptr res, gr_srcptr initial, int subtract, gr_srcptr v
int
gr_generic_vec_set_powers(gr_ptr res, gr_srcptr x, slong len, gr_ctx_t ctx)
{
int status = GR_SUCCESS;
slong sz = ctx->sizeof_elem;
if (len <= 0) return status;
status |= gr_one(GR_ENTRY(res, 0, sz), ctx);
if (len <= 1) return status;
status |= gr_set(GR_ENTRY(res, 1, sz), x, ctx);
if (len <= 2) return status;

gr_method_binary_op mul = GR_BINARY_OP(ctx, MUL);
gr_method_unary_op sqr = GR_UNARY_OP(ctx, SQR);
int status = GR_SUCCESS;
slong i;
slong sz = ctx->sizeof_elem;;

for (i = 0; i < len; i++)
/* Prefer squaring for powers? */
if (gr_ctx_is_finite(ctx) == T_TRUE || gr_ctx_has_real_prec(ctx) == T_TRUE)
{
if (i == 0)
status |= gr_one(GR_ENTRY(res, i, sz), ctx);
else if (i == 1)
status |= gr_set(GR_ENTRY(res, i, sz), x, ctx);
else if (i % 2 == 0)
status |= sqr(GR_ENTRY(res, i, sz), GR_ENTRY(res, i / 2, sz), ctx);
else
status |= mul(GR_ENTRY(res, i, sz), GR_ENTRY(res, i - 1, sz), x, ctx);
for (i = 2; i < len; i++)
{
if (i % 2 == 0)
status |= sqr(GR_ENTRY(res, i, sz), GR_ENTRY(res, i / 2, sz), ctx);
else
status |= mul(GR_ENTRY(res, (i + 1) / 2, sz), GR_ENTRY(res, i / 2, sz), x, ctx);
}
}
else
for (i = 2; i < len; i++)
status |= mul(GR_ENTRY(res, i, sz), GR_ENTRY(res, i - 1, sz), x, ctx);

return status;
}
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62 changes: 54 additions & 8 deletions src/gr_poly/compose.c
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Expand Up @@ -13,6 +13,7 @@

#include "gr_vec.h"
#include "gr_poly.h"
#include "longlong.h"

/* compose by poly2 = a*x^n + c, no aliasing; n >= 1 */
static int
Expand All @@ -39,19 +40,64 @@ _gr_poly_compose_axnc(gr_ptr res, gr_srcptr poly1, slong len1,
}
else
{
int maxbit = FLINT_CLOG2(len1);
gr_ptr t;
GR_TMP_INIT(t, ctx);

status |= gr_set(t, a, ctx);

for (i = 1; i < len1; i++)
/* Prefer squaring for powers? cf. _gr_vec_set_powers */
if (gr_ctx_is_finite(ctx) == T_TRUE || gr_ctx_has_real_prec(ctx) == T_TRUE)
{
status |= gr_mul(GR_ENTRY(res, i, sz), GR_ENTRY(res, i, sz), t, ctx);
if (i + 1 < len1)
status |= gr_mul(t, t, a, ctx);
GR_TMP_INIT_VEC(t, maxbit, ctx);

status |= gr_set(GR_ENTRY(t, 0, sz), a, ctx);
status |= gr_mul(GR_ENTRY(res, 1, sz), GR_ENTRY(res, 1, sz), a, ctx);
for (int j = 1; j < maxbit; ++j)
{
status |= gr_sqr(GR_ENTRY(t, j, sz), GR_ENTRY(t, j-1, sz), ctx);
status |= gr_mul(GR_ENTRY(res, 1<<j, sz), GR_ENTRY(res, 1<<j, sz), GR_ENTRY(t, j, sz), ctx);
}
for (i = ((slong) 1 << (maxbit-1)) + 1; i < len1; i++)
{
int bit = flint_ctz(i);
status |= gr_mul(GR_ENTRY(t, maxbit-1-bit, sz), GR_ENTRY(t, maxbit-1-bit, sz), a, ctx);
status |= gr_mul(GR_ENTRY(res, i>>bit, sz), GR_ENTRY(res, i>>bit, sz), GR_ENTRY(t, maxbit-1-bit, sz), ctx);

for (int j = bit; j > 0; --j)
{
status |= gr_sqr(GR_ENTRY(t, maxbit-j, sz), GR_ENTRY(t, maxbit-j-1, sz), ctx);
status |= gr_mul(GR_ENTRY(res, i>>(j-1), sz), GR_ENTRY(res, i>>(j-1), sz), GR_ENTRY(t, maxbit-j, sz), ctx);
}
}

for (i = (len1 + 1) >> 1; i < ((slong)1 << (maxbit-1)); i++)
{
int bit = flint_ctz(i);
status |= gr_mul(GR_ENTRY(t, maxbit-2-bit, sz), GR_ENTRY(t, maxbit-2-bit, sz), a, ctx);
status |= gr_mul(GR_ENTRY(res, i>>bit, sz), GR_ENTRY(res, i>>bit, sz), GR_ENTRY(t, maxbit-2-bit, sz), ctx);

for (int j = bit; j > 0; --j)
{
status |= gr_sqr(GR_ENTRY(t, maxbit-j-1, sz), GR_ENTRY(t, maxbit-j-2, sz), ctx);
status |= gr_mul(GR_ENTRY(res, i>>(j-1), sz), GR_ENTRY(res, i>>(j-1), sz), GR_ENTRY(t, maxbit-j-1, sz), ctx);
}
}

GR_TMP_CLEAR_VEC(t, maxbit, ctx);
}
else
{
GR_TMP_INIT(t, ctx);

status |= gr_set(t, a, ctx);

GR_TMP_CLEAR(t, ctx);
for (i = 1; i < len1; i++)
{
status |= gr_mul(GR_ENTRY(res, i, sz), GR_ENTRY(res, i, sz), t, ctx);
if (i + 1 < len1)
status |= gr_mul(t, t, a, ctx);
}

GR_TMP_CLEAR(t, ctx);
}
}
}

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2 changes: 1 addition & 1 deletion src/gr_poly/compose_series_brent_kung.c
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Expand Up @@ -46,7 +46,7 @@ _gr_poly_compose_series_brent_kung(gr_ptr res, gr_srcptr poly1, slong len1,
status |= _gr_vec_set(Brow(i), GR_ENTRY(poly1, i * m, sz), m, ctx);
status |= _gr_vec_set(Brow(i), GR_ENTRY(poly1, i * m, sz), len1 % m, ctx);

/* Set rows of A to powers of poly2 */
/* Set rows of A to powers of poly2 (cf. _gr_vec_set_powers) */
status |= gr_one(Arow(0), ctx);
status |= _gr_vec_set(Arow(1), poly2, len2, ctx);

Expand Down
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