From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Thu, 8 Aug 2019 01:07:07 +0000 (+0100)
Subject: clarify
X-Git-Tag: convert-csv-opcode-to-binary~4257
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=59cdf7a9c73f71f696bccac8d95b21bf3def16ee;p=libreriscv.git

clarify
---

diff --git a/ztrans_proposal.mdwn b/ztrans_proposal.mdwn
index 04694181f..578015bae 100644
--- a/ztrans_proposal.mdwn
+++ b/ztrans_proposal.mdwn
@@ -10,12 +10,14 @@ See:
 Extension subsets:
 
 * **Zftrans**: standard transcendentals (best suited to 3D)
-* **ZftransExt**: extra functions (useful, not generally needed for 3D, can be synthesised using Ztrans)
+* **ZftransExt**: extra functions (useful, not generally needed for 3D,
+  can be synthesised using Ztrans)
 * **Ztrigpi**: trig. xxx-pi sinpi cospi tanpi
 * **Ztrignpi**: trig non-xxx-pi sin cos tan
 * **Zarctrigpi**: arc-trig. a-xxx-pi: atan2pi asinpi acospi
 * **Zarctrignpi**: arc-trig. non-a-xxx-pi: atan2, asin, acos
-* **Zfhyp**: hyperbolic/inverse-hyperbolic.  sinh, cosh, tanh, asinh, acosh, atanh
+* **Zfhyp**: hyperbolic/inverse-hyperbolic.  sinh, cosh, tanh, asinh,
+  acosh, atanh (can be synthesised - see below)
 * **ZftransAdv**: much more complex to implement in hardware
 
 Minimum recommended requirements for 3D: Zftrans, Ztrigpi, Zarctrigpi,
@@ -76,7 +78,7 @@ FACOSH   | inverse hyperbolic cos   | rd = acosh(rs1)         | Zfhyp |
 FATANH   | inverse hyperbolic tan   | rd = atanh(rs1)         | Zfhyp |
 """]]
 
-# Pseudo-code ops and macro-ops
+# Synthesis, Pseudo-code ops and macro-ops
 
 The pseudo-ops are best left up to the compiler rather than being actual
 pseudo-ops, by allocating one scalar FP register for use as a constant
@@ -99,11 +101,13 @@ Hypotenuse example (obviates need for Zfhyp except for high-performance):
 
     ASINH( x ) = ln( x + SQRT(x**2+1)
 
-# To evaluate: should LOG be replaced with LOG1P (and EXP with EXPM1)?
+LOG / LOGP1 example:
 
     LOG(x) = LOGP1(x) + 1.0
     EXP(x) = EXPM1(x-1.0)
 
+# To evaluate: should LOG be replaced with LOG1P (and EXP with EXPM1)?
+
 RISC principle says "exclude LOG because it's covered by LOGP1 plus an ADD".
 Research needed to ensure that implementors are not compromised by such
 a decision