From: Iago Toral Quiroga <ito...@igalia.com>
At least i965 hardware does not have native support for truncating doubles.
---
src/compiler/nir/nir.h | 1 +
src/compiler/nir/nir_lower_double_ops.c | 83 +++++++++++++++++++++++++++++++++
2 files changed, 84 insertions(+)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 434d92b..f83b2e0 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2286,6 +2286,7 @@ typedef enum {
nir_lower_drcp = (1 << 0),
nir_lower_dsqrt = (1 << 1),
nir_lower_drsq = (1 << 2),
+ nir_lower_dtrunc = (1 << 3),
} nir_lower_doubles_options;
void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options);
diff --git a/src/compiler/nir/nir_lower_double_ops.c
b/src/compiler/nir/nir_lower_double_ops.c
index 4cd153c..9eec858 100644
--- a/src/compiler/nir/nir_lower_double_ops.c
+++ b/src/compiler/nir/nir_lower_double_ops.c
@@ -302,6 +302,81 @@ lower_sqrt_rsq(nir_builder *b, nir_ssa_def *src, bool sqrt)
return res;
}
+static nir_ssa_def *
+lower_trunc(nir_builder *b, nir_ssa_def *src)
+{
+ nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b, src),
+ nir_imm_int(b, 1023));
+
+ nir_ssa_def *frac_bits = nir_isub(b, nir_imm_int(b, 52), unbiased_exp);
+
+ /*
+ * Depending on the exponent, we compute a mask with the bits we need to
+ * remove in order to trunc the double. The mask is computed like this:
+ *
+ * if (unbiased_exp < 0)
+ * mask = 0x0
+ * else if (unbiased_exp > 52)
+ * mask = 0x7fffffffffffffff
+ * else
+ * mask = (1LL < frac_bits) - 1
+ *
+ * Notice that the else branch is a 64-bit integer operation that we need
+ * to implement in terms of 32-bit integer arithmetics (at least until we
+ * support 64-bit integer arithmetics).
+ */
+
+ /* Compute "mask = (1LL << frac_bits) - 1" in terms of hi/lo 32-bit chunks
+ * for the else branch
+ */
+ nir_ssa_def *mask_lo =
+ nir_bcsel(b,
+ nir_ige(b, frac_bits, nir_imm_int(b, 32)),
+ nir_imm_int(b, 0xffffffff),
+ nir_isub(b,
+ nir_ishl(b,
+ nir_imm_int(b, 1),
+ frac_bits),
+ nir_imm_int(b, 1)));
+
+ nir_ssa_def *mask_hi =
+ nir_bcsel(b,
+ nir_ilt(b, frac_bits, nir_imm_int(b, 33)),
+ nir_imm_int(b, 0),
+ nir_isub(b,
+ nir_ishl(b,
+ nir_imm_int(b, 1),
+ nir_isub(b,
+ frac_bits,
+ nir_imm_int(b, 32))),
+ nir_imm_int(b, 1)));
+
+ /* Compute the correct mask to use based on unbiased_exp */
+ nir_ssa_def *mask =
+ nir_bcsel(b,
+ nir_ilt(b, unbiased_exp, nir_imm_int(b, 0)),
+ nir_pack_double_2x32_split(b,
+ nir_imm_int(b, 0xffffffff),
+ nir_imm_int(b, 0x7fffffff)),
+ nir_bcsel(b, nir_ige(b, unbiased_exp, nir_imm_int(b, 53)),
+ nir_imm_double(b, 0.0),
+ nir_pack_double_2x32_split(b, mask_lo, mask_hi)));
+
+ /* Mask off relevant mantissa bits (0..31 in the low 32-bits
+ * and 0..19 in the high 32 bits)
+ */
+ mask_lo = nir_unpack_double_2x32_split_x(b, mask);
+ mask_hi = nir_unpack_double_2x32_split_y(b, mask);
+
+ nir_ssa_def *src_lo = nir_unpack_double_2x32_split_x(b, src);
+ nir_ssa_def *src_hi = nir_unpack_double_2x32_split_y(b, src);
+
+ nir_ssa_def *zero = nir_imm_int(b, 0);
+ nir_ssa_def *new_src_lo = nir_bfi(b, mask_lo, zero, src_lo);
+ nir_ssa_def *new_src_hi = nir_bfi(b, mask_hi, zero, src_hi);
+ return nir_pack_double_2x32_split(b, new_src_lo, new_src_hi);
+}
+
static void
lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options)
{
@@ -325,6 +400,11 @@ lower_doubles_instr(nir_alu_instr *instr,
nir_lower_doubles_options options)
return;
break;
+ case nir_op_ftrunc:
+ if (!(options & nir_lower_dtrunc))
+ return;
+ break;
+
default:
return;
}
@@ -348,6 +428,9 @@ lower_doubles_instr(nir_alu_instr *instr,
nir_lower_doubles_options options)
case nir_op_frsq:
result = lower_sqrt_rsq(&bld, src, false);
break;
+ case nir_op_ftrunc:
+ result = lower_trunc(&bld, src);
+ break;
default:
unreachable("unhandled opcode");
}
--
2.5.0
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