vc4: Apply a Newton-Raphson step to improve RCP.
Fixes all the piglit floating-point *-op-div tests, among others.
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@ -296,6 +296,22 @@ tgsi_to_qir_scalar(struct vc4_compile *c,
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return dst;
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}
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static struct qreg
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tgsi_to_qir_rcp(struct vc4_compile *c,
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struct tgsi_full_instruction *tgsi_inst,
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enum qop op, struct qreg *src, int i)
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{
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struct qreg x = src[0 * 4 + 0];
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struct qreg r = qir_RCP(c, x);
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/* Apply a Newton-Raphson step to improve the accuracy. */
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r = qir_FMUL(c, r, qir_FSUB(c,
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qir_uniform_f(c, 2.0),
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qir_FMUL(c, x, r)));
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return r;
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}
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static struct qreg
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qir_srgb_decode(struct vc4_compile *c, struct qreg srgb)
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{
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@ -1165,7 +1181,7 @@ emit_tgsi_instruction(struct vc4_compile *c,
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[TGSI_OPCODE_CMP] = { 0, tgsi_to_qir_cmp },
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[TGSI_OPCODE_MAD] = { 0, tgsi_to_qir_mad },
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[TGSI_OPCODE_RCP] = { QOP_RCP, tgsi_to_qir_scalar },
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[TGSI_OPCODE_RCP] = { QOP_RCP, tgsi_to_qir_rcp },
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[TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_scalar },
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[TGSI_OPCODE_EX2] = { QOP_EXP2, tgsi_to_qir_scalar },
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[TGSI_OPCODE_LG2] = { QOP_LOG2, tgsi_to_qir_scalar },
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