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Russ Cox a4d0269a4f math/big: use clearer loop bounds check elimination 
Checking that the lengths are equal and panicking teaches the compiler
that it can assume “i in range for z” implies “i in range for x”, letting us
simplify the actual loops a bit.

It also turns up a few places in math/big that were playing maybe a little
too fast and loose with slice lengths. Update those to explicitly set all the
input slices to the same length.

These speedups are basically irrelevant, since they only happen
in real code if people are compiling with -tags math_big_pure_go.
But at least the code is clearer.

benchmark \ system                   c3h88    c2s16       s7      386   s7-386   c4as16      mac      arm  loong64  ppc64le  riscv64    s390x
AddVV/words=1/impl=go                    ~  +11.20%   +5.11%   -7.67%   -7.77%   +1.90%  +10.76%  -33.22%        ~  +10.98%        ~   +6.60%
AddVV/words=10/impl=go             -22.12%  -13.48%  -10.37%  -17.95%  -18.07%  -24.58%  -22.04%  -29.95%  -14.22%        ~   -6.33%   +3.66%
AddVV/words=16/impl=go              -9.75%  -13.73%        ~  -21.90%  -18.66%  -30.03%  -20.45%  -28.09%  -17.33%   -7.15%   -8.96%  +12.55%
AddVV/words=100/impl=go             -5.91%   -1.02%        ~  -29.23%  -22.18%  -25.62%   -6.49%  -23.59%  -22.31%   -1.88%  -14.13%   +9.23%
AddVV/words=1000/impl=go            -0.52%   -0.19%   -3.58%  -33.89%  -23.46%  -22.46%        ~  -24.00%  -24.73%   +0.93%  -15.79%  +12.32%
AddVV/words=10000/impl=go                ~        ~        ~  -33.79%  -23.72%  -23.79%   -5.98%  -23.92%        ~   +0.78%  -15.45%   +8.59%
AddVV/words=100000/impl=go               ~        ~        ~  -33.90%  -24.25%  -22.82%   -4.09%  -24.63%        ~   +1.00%  -13.56%        ~
SubVV/words=1/impl=go                    ~  +11.64%  +14.05%        ~   -4.07%        ~  +10.79%  -33.69%        ~        ~   +3.89%  +12.33%
SubVV/words=10/impl=go             -10.31%  -14.09%   -7.38%  +13.76%  -13.25%  -18.05%  -20.08%  -24.97%  -14.15%  +10.13%   -0.97%   -2.51%
SubVV/words=16/impl=go              -8.06%  -13.73%   -5.70%  +17.00%  -12.83%  -23.76%  -17.52%  -25.25%  -17.30%   -2.80%   -4.96%  -18.25%
SubVV/words=100/impl=go             -9.22%   -1.30%   -2.76%  +20.88%  -14.35%  -15.29%   -8.49%  -19.64%  -22.31%   -0.68%  -14.30%   -9.04%
SubVV/words=1000/impl=go            -0.60%        ~   -3.43%  +23.08%  -16.14%  -11.96%        ~  -28.52%  -24.73%        ~  -15.95%   -9.91%
SubVV/words=10000/impl=go                ~        ~        ~  +26.01%  -15.24%  -11.92%        ~  -28.26%   +4.25%        ~  -15.42%   -5.95%
SubVV/words=100000/impl=go               ~        ~        ~  +25.71%  -15.83%  -12.13%        ~  -27.88%   -1.27%        ~  -13.57%   -6.72%
LshVU/words=1/impl=go               +0.56%   +0.36%        ~        ~        ~        ~        ~        ~        ~        ~        ~        ~
LshVU/words=10/impl=go             +13.37%   +4.63%        ~        ~        ~        ~        ~   -2.90%        ~        ~        ~        ~
LshVU/words=16/impl=go             +22.83%   +6.47%        ~        ~        ~        ~        ~        ~   +0.80%        ~        ~   +5.88%
LshVU/words=100/impl=go             +7.56%  +13.95%        ~        ~        ~        ~        ~        ~   +0.33%   -2.50%        ~        ~
LshVU/words=1000/impl=go            +0.64%  +17.92%        ~        ~        ~        ~        ~   -6.52%        ~   -2.58%        ~        ~
LshVU/words=10000/impl=go                ~  +17.60%        ~        ~        ~        ~        ~   -6.64%   -6.22%   -1.40%        ~        ~
LshVU/words=100000/impl=go               ~  +14.57%        ~        ~        ~        ~        ~        ~   -5.47%        ~        ~        ~
RshVU/words=1/impl=go                    ~        ~        ~        ~        ~        ~        ~        ~        ~        ~        ~   +2.72%
RshVU/words=10/impl=go                   ~        ~        ~        ~        ~        ~        ~   +2.50%        ~        ~        ~        ~
RshVU/words=16/impl=go                   ~   +0.53%        ~        ~        ~        ~        ~   +3.82%        ~        ~        ~        ~
RshVU/words=100/impl=go                  ~        ~        ~        ~        ~        ~        ~   +6.18%        ~        ~        ~        ~
RshVU/words=1000/impl=go                 ~        ~        ~        ~        ~        ~        ~   +7.00%        ~        ~        ~        ~
RshVU/words=10000/impl=go                ~        ~        ~        ~        ~        ~        ~        ~        ~        ~        ~        ~
RshVU/words=100000/impl=go               ~        ~        ~        ~        ~        ~        ~   +7.05%        ~        ~        ~        ~
MulAddVWW/words=1/impl=go          -10.34%   +4.43%  +10.62%   -1.62%   -4.74%   -2.86%  +11.75%        ~   -8.00%   +8.89%   +3.87%        ~
MulAddVWW/words=10/impl=go          -1.61%   -5.87%        ~   -8.30%   -4.55%   +0.87%        ~   -5.28%  -20.82%        ~        ~   -2.32%
MulAddVWW/words=16/impl=go          -2.96%   -5.28%        ~   -9.22%   -5.28%        ~        ~   -3.74%  -19.52%   -1.48%   -2.53%   -9.52%
MulAddVWW/words=100/impl=go         -3.89%   -7.53%   +1.93%  -10.49%   -4.87%   -8.27%        ~        ~   -0.65%   -0.61%   -7.59%  -20.61%
MulAddVWW/words=1000/impl=go        -0.45%   -3.91%   +4.54%  -11.46%   -4.69%   -8.53%        ~        ~   -0.05%        ~   -8.88%  -19.77%
MulAddVWW/words=10000/impl=go            ~   -3.30%   +4.10%  -11.34%   -4.10%   -9.43%        ~   -0.61%        ~   -0.55%   -8.21%  -18.48%
MulAddVWW/words=100000/impl=go      -0.30%   -3.03%   +4.31%  -11.55%   -4.41%   -9.74%        ~   -0.75%   +0.63%        ~   -7.80%  -19.82%
AddMulVVWW/words=1/impl=go               ~  +13.09%  +12.50%   -7.05%  -10.41%   +2.53%  +13.32%   -3.49%        ~  +15.56%   +3.62%        ~
AddMulVVWW/words=10/impl=go        -15.96%   -9.06%   -5.06%  -14.56%  -11.83%   -5.44%  -26.30%  -14.23%  -11.44%   -1.79%   -5.93%   -6.60%
AddMulVVWW/words=16/impl=go        -19.05%  -12.43%   -6.19%  -14.24%  -12.67%   -8.65%  -18.64%  -16.56%  -10.64%   -3.00%   -7.61%  -12.80%
AddMulVVWW/words=100/impl=go       -22.13%  -16.59%  -13.04%  -13.79%  -11.46%  -12.01%   -6.46%  -21.80%   -5.08%   -3.13%  -13.60%  -22.53%
AddMulVVWW/words=1000/impl=go      -17.07%  -17.05%  -14.08%  -13.59%  -12.13%  -11.21%        ~  -22.81%   -4.27%   -1.27%  -16.35%  -23.47%
AddMulVVWW/words=10000/impl=go     -15.03%  -16.78%  -14.23%  -13.86%  -11.84%  -11.69%        ~  -22.75%  -13.39%   -1.10%  -14.37%  -22.01%
AddMulVVWW/words=100000/impl=go    -13.70%  -14.90%  -14.26%  -13.55%  -12.04%  -11.63%        ~  -22.61%        ~   -2.53%  -10.42%  -23.16%

Change-Id: Ic6f64344484a762b818c7090d1396afceb638607
Reviewed-on: https://go-review.googlesource.com/c/go/+/665155
Auto-Submit: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
 		2025-04-19 08:19:27 -07:00
..
big math/big: use clearer loop bounds check elimination 2025-04-19 08:19:27 -07:00
bits math/bits: update reference to debruijn paper 2024-12-04 22:15:36 +00:00
cmplx math: add available godoc link 2023-10-19 11:59:09 +00:00
rand all: surround -test.run arguments with ^$ 2025-02-25 10:58:29 -08:00
abs.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
acos_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
acosh.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
acosh_s390x.s
…
all_test.go math: add large exact float rounding tests 2024-09-04 13:36:10 +00:00
arith_s390x.go
…
arith_s390x_test.go
…
asin.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
asin_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
asinh.go all: fix mismatched symbols 2023-06-13 20:02:49 +00:00
asinh_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
atan.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
atan2.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
atan2_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
atan_s390x.s
…
atanh.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
atanh_s390x.s all: replace leading spaces with tabs in assembly 2023-03-23 20:52:57 +00:00
bits.go all: replace `` and '' with “ (U+201C) and ” (U+201D) in doc comments 2022-04-05 17:52:29 +00:00
cbrt.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
cbrt_s390x.s
…
const.go math: show value of integer constants in comments 2022-09-21 14:07:39 +00:00
const_test.go
…
copysign.go math: improve documentation of Copysign 2022-04-14 17:42:53 +00:00
cosh_s390x.s
…
dim.go math: document that Min/Max differ from min/max 2023-06-15 19:45:12 +00:00
dim_amd64.s
…
dim_arm64.s
…
dim_asm.go cmd/compile, math: improve implementation of math.{Max,Min} on loong64 2024-08-07 01:16:28 +00:00
dim_loong64.s cmd/compile, math: improve implementation of math.{Max,Min} on loong64 2024-08-07 01:16:28 +00:00
dim_noasm.go cmd/compile, math: improve implementation of math.{Max,Min} on loong64 2024-08-07 01:16:28 +00:00
dim_riscv64.s
…
dim_s390x.s
…
erf.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
erf_s390x.s
…
erfc_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
erfinv.go math: add available godoc link 2023-10-19 11:59:09 +00:00
example_test.go
…
exp.go math: add available godoc link 2023-10-19 11:59:09 +00:00
exp2_asm.go math: implement func archExp and archExp2 in assembly on loong64 2025-03-05 18:30:54 -08:00
exp2_noasm.go math: implement func archExp and archExp2 in assembly on loong64 2025-03-05 18:30:54 -08:00
exp_amd64.go
…
exp_amd64.s
…
exp_arm64.s
…
exp_asm.go math: implement func archExp and archExp2 in assembly on loong64 2025-03-05 18:30:54 -08:00
exp_loong64.s math: implement func archExp and archExp2 in assembly on loong64 2025-03-05 18:30:54 -08:00
exp_noasm.go math: implement func archExp and archExp2 in assembly on loong64 2025-03-05 18:30:54 -08:00
exp_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
expm1.go math: add available godoc link 2023-10-19 11:59:09 +00:00
expm1_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
export_s390x_test.go
…
export_test.go
…
floor.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
floor_386.s
…
floor_amd64.s
…
floor_arm64.s
…
floor_asm.go math: implement arch{Floor, Ceil, Trunc} in hardware on loong64 2024-10-12 03:24:22 +00:00
floor_loong64.s math: implement arch{Floor, Ceil, Trunc} in hardware on loong64 2024-10-12 03:24:22 +00:00
floor_noasm.go math: implement arch{Floor, Ceil, Trunc} in hardware on loong64 2024-10-12 03:24:22 +00:00
floor_ppc64x.s all: drop old +build lines 2023-10-19 23:33:27 +00:00
floor_riscv64.s math: add round assembly implementations on riscv64 2024-09-11 02:28:10 +00:00
floor_s390x.s
…
floor_wasm.s
…
fma.go math: fix portable FMA when x*y < 0 and x*y == -z 2023-07-05 22:05:30 +00:00
frexp.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
gamma.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
huge_test.go math: enable huge argument tests on s390x 2023-07-31 16:23:41 +00:00
hypot.go math: add available godoc link 2023-10-19 11:59:09 +00:00
hypot_386.s
…
hypot_amd64.s
…
hypot_asm.go
…
hypot_noasm.go
…
j0.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
j1.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
jn.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
ldexp.go math: add available godoc link 2023-10-19 11:59:09 +00:00
lgamma.go math: add available godoc link 2023-10-19 11:59:09 +00:00
log.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
log1p.go math: add available godoc link 2023-10-19 11:59:09 +00:00
log1p_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
log10.go math: add available godoc link 2023-10-19 11:59:09 +00:00
log10_s390x.s
…
log_amd64.s all: replace leading spaces with tabs in assembly 2023-03-23 20:52:57 +00:00
log_asm.go
…
log_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
log_stub.go
…
logb.go math: fix function name in comment 2022-11-07 19:46:45 +00:00
mod.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
modf.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
modf_arm64.s
…
modf_asm.go
…
modf_noasm.go
…
modf_ppc64x.s all: drop old +build lines 2023-10-19 23:33:27 +00:00
nextafter.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
pow.go math: handle int64 overflows for odd integer exponents in Pow(-0, y) 2023-01-24 19:10:58 +00:00
pow10.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
pow_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
remainder.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
signbit.go
…
sin.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
sin_s390x.s math: huge argument handling for sin/cos in s390x 2023-07-31 04:25:54 +00:00
sincos.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
sinh.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
sinh_s390x.s
…
sqrt.go cmd/compile,math: remove all sqrt assembly code 2022-08-15 17:07:57 +00:00
stubs.go
…
stubs_s390x.s
…
tan.go all: fix some lint issues 2022-05-08 17:27:54 +00:00
tan_s390x.s cmd/asm: add LCDBR instruction on s390x 2025-03-24 07:05:55 -07:00
tanh.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
tanh_s390x.s
…
trig_reduce.go all: gofmt main repo 2022-04-11 16:34:30 +00:00
unsafe.go all: document legacy //go:linkname for final round of modules 2024-05-29 17:58:53 +00:00